Apparatus for accurately measuring the volume of a meter prover

ABSTRACT

Apparatus and method are disclosed for measuring the volume of a chamber of a meter prover. The meter prover includes a piston adapted for rectilinear movement within said cylinder between a first position and a second position. The volume measuring apparatus comprises an antenna disposed within the chamber and a generator coupled to apply electromagnetic energy to the antenna whereby electromagnetic waves are emanated into the chamber. A detector is coupled to the antenna to detect electromagnetic energy reflected from the chamber and is in turn coupled to a resonant detector in the form of a cathode ray tube, whereby a minimum of the level of the electromagnetic energy may be determined. Further, a frequency detector in the form of a counter, is connected to the output of the generator to detect the frequencies of the generator output at which the minimum level occurs as observed upon a display device corresponding to the establishment of a resonant standing wave within the chamber of the meter prover. The frequency(ies) at which the resonant standing waves are established within the chamber, in turn determine the volume of the meter prover chamber. The electromagnetic field(s) are generated within the chamber of a mode selected so that at a resonant condition within the chamber, the electric and magnetic component fields of the electromagnetic field have a defined relation to the dimensions of the chamber of regular geometry, illustratively, a right circular cylinder.

I. DESCRIPTION Background of Prior Art

This invention, in its preferred form, relates to meter provers fortesting the accuracy of fluid and in particular gas meters.

In the prior art, U.S. Pat. No. 185,319 of Harris is an early example ofthe use of a bell-type meter prover comprising a bell-shaped containeror bell that is rectilinearly moved into and from a container or kettlefilled with a liquid such as oil. Typically, a pulley arrangement isused whereby a pulley is located above the bell, with a cord suspendedabout the pulley having one end attached to the bell and the other endto a set of weights. A conduit is provided from the bell to the meter tobe tested, whereby as the bell is drawn upward, a fluid, e.g., gas, isdrawn through the meter and into the bell. A valve is placed within theconduit and when disposed to its closed position, prevents the flow ofthe fluid from the meter into the space defined by the bell and itskettle, thus inhibiting the motion of the bell and the weight suspendedtherefrom by the pulley. Upon opening of the valve, the fluid flows intothe bell permitting the weights to exert its force upon the bell,thereby lifting the bell. When the weights are released, the cord andthus the bell are pulled upward, thus creating a vacuum within the bell,the oil providing a seal to prevent leakage of air otherwise into thebell.

In order to determine the amount of fluid that is drawn through themeter, the early practice sought to control the extent of movement ofthe bell, correlating this movement to a given quantity of fluid thatwould be drawn through the meter and comparing the known quantity offluid drawn through the meter and into the meter prover, to the fluid asmeasured by the meter, typically indicated by the meter's dialpositions. Current methods require physical measurements of thedimensions of the bell (bell strapping) which are inconvenient and aresubject to a number of possible errors incurred by averaging thenon-uniform geometrical diameters and the wall thicknesses of the belland by interpolating the scale markings by eye. The quoted accuracy ofsuch current methods is about 0.3% at best. Thus, it can be seen thatsuch a bell-type meter prover, which was the calibrating standard forfluid meters, lacked inherently a high degree of accuracy due to theerrors introduced by (1) the visual sightings of the beginning and finalpoints of the bell movement, (2) the visual sightings of the initial andterminating volume indications by the meter dial, and (3) the inherentinaccuracy of determining the volume of the bell. The most significantcause of error in this technique was due to the difficulty of accuratelymeasuring and determining the volume of the bell. The bell, itself, wasformed with as great an accuracy as possible, but variations in itsdiameter, and therefore circumference, inherently occurred. The takingof many measurements of the circumference by bell strapping was the bestmethod then devised to obtain the bell's average circumference andtherefrom the volume of the cylindrical portion of the bell.

The use of the bell-type prover has persisted for many years withimprovements being made thereto primarily in the nature of determiningthe movement of the bell and in determining the volume of fluid passedthrough the meter. One of the earliest examples of an automated proversystem is found in U.S. Pat. No. 3,050,980 of Dufour et al., whichdiscloses a bell having optical pick offs to sense the movement of itsbell as it is directed upwardly by its motor. A conduit is directed fromthe bell to the meter having a first solenoid actuated valve forcontrolling the flow of fluid from the meter to the bell, as well as asecond solenoid actuated valve coupled to the conduit for permittingdischarge of the fluid from the bell as it returns to its downmostposition. In operation, the bell, initially filled with air, is loweredinto its tank tending to drive air through the meter. A dial hand on themeter register, known as the "prover hand" is detected by means of anoptical pick-up to initiate the test, whereby the first valve is opened,while maintaining the second valve closed, to permit a flow of the fluidfrom the bell through the meter. An automatic airtight test is describedwherein both the first inlet and second discharge valves are closed, andas pressure is built up, tests are made for leaks in the system and itsvalves by measuring the pressure established within the bell.

Further, U.S. Pat. No. 2,987,911 of McDonell suggests a prover system inwhich first and second temperature sensors are disposed at the outletsof the meter and of the prover, respectively, whereby the temperaturedifferences is calculated to develop a temperature compensation factorTc, which is used to make a correction in the calculated volume.

As suggested by U.S. Pat. No. 3,933,027 of Mehall, efforts were made toimprove the bell-type prover system by automating its operation. TheMehall patent '027 suggests the placement of a series of sensing flagswith respect to its bell, whereby an optical encoder senses the movementof these flags to provide indications of corresponding volumes of air asdrawn by the bell's prover through the coupled meter. Further, a secondoptical encoder is coupled to the dial of the meter to provide an outputas a train of pulses indicative of the volume flowing through the meter.At initiation of the meter test, a gate is activated by the firstoptical encoder to initiate a counting or timing procedure whereby aclock signal is applied to each of a bell clock counter and a meterclock counter. The gate passing the clock signals to the bell counter isdisabled upon reaching a given count corresponding to a known quantityof fluid as drawn through the meter. When a similar quantity of fluidhas been measured by the meter, as indicated by the second opticalencoder, a signal therefrom is applied to a gate to terminate theapplication of clock signals to the meter clock counter. At termination,first and second counts have been accumulated within the bell clock andmeter clock counters, whereby the ratio thereof may be readilycalculated and displayed upon a suitable digital display. This ratio isunderstood to be the meter registration, i.e., the ratio of the actualor calibrated volume of fluid passed through the meter to that measuredby the meter.

U.S. Pat. No. 3,937,048 of St. Clair et al provides similar teachings tothe Mehall patent '027 disclosing a bell-type automatic meter proverwherein there is further included a device for sensing the series ofpulses produced by the meter during a cycle of its operation. The volumeactually passed through the meter is measured by an encoder whichproduces a train of pulses indicative of the linear movement of the belland therefore the volume displaced into or out of the bell during atest. The encoder provides a train of pulses indicative of the volumedisplaced by the bell; the encoder pulses are accumulated for a givennumber of meter operation cycles, to calibrate the meter indication ofvolume with a known volume of fluid displaced by the bell.

U.S. Pat. No. 3,877,287 of Duntz, Jr. suggests a substantially differentstructure, wherein in place of the bell-type container, a cylinder isused to receive a piston driven through the cylinder at a controlledrate by a motor rotatively coupled by a lead screw to the piston fordriving it through the cylinder as the motor rotates. As a result, thepiston is driven at a constant velocity through the precision bore tubeor cylinder to drive fluid from the cylinder and through the meter to betested. The Duntz, Jr. patent '287 suggests two ways of measuring thefluid flow rate, the first involving placing a series of holes in apiston rod interconnecting the piston and the lead screw, and sensingthe movement of the holes past a photodetector. A second method uses anoptical encoder coupled to the drive motor to provide an output train ofpulses indicative of piston displacement and therefore the actual fluidvolume displaced from the cylinder.

U.S. Pat. No. 3,631,709 of Smith also discloses a meter provercomprising a piston and cylinder arrangement, wherein the piston isdriven via a lead screw by a program controlled motor. Upon actuation,the motor drives via the lead screw the piston through the cylinder,whereby a known volume of fluid (water) is drawn through a series ofmeters disposed in series. The control program of the motor causes thepiston to move at different rates of speed, whereby corresponding fluidflow rates are established through the meters for a single strobe of thepiston through the cylinder. A magnet is coupled to a shaftinterconnecting the lead screw and the piston to actuate a reed switchas the piston is drawn through the cylinder, to initiate the counting ofpulses derived from a first or master pulser 54 coupled to the motor.The output of the master pulser is a train of pulses and is applied to aregister to provide an indication of the actual flow through the meters.Optical encoders are also coupled to each of the meters to provide pulsesignals to a second set of registers whereby the measured values offluid flow measured by the meters may be accumulated and displayed. Thestandard or actual volume of flow is defined as a specific number ofcounts from the first or master pulser against which the output from theindividual meters is compared. The program control of the motor permitsthe acceleration of the motor and its piston to a steady state conditionbefore beginning measurement of the fluid flow through the meter inorder to permit any transients in the fluid to settle.

As indicated above, the prior art has dealt with providing automation tothe process of testing meters by automatically initiating andterminating the counting of pulses from a first encoder indicative ofthe standard volume of fluid drawn through the meter, as well as thecounting of pulses from a second encoder indicative of the volume offluid measured by the meter under test.

However, the prior art has not dealt with the problem of improving thebasic accuracy of the meter prover, i.e., the basic meter calibratingdevice. At this point in the development of the art, meter provers,particularly those of the bell-type, are only able to achieve anaccuracy of ±0.2% under optimum conditions. It is thus obvious that thefluid meters calibrated or tested with such provers may achieve nogreater accuracy themselves. One of the primary reasons for the lack ofultimate precision in existing meter provers, is the lack of precisemethods of and apparatus for measuring with high precision the volumedisplaced within either the bell or the cylinder as disclosed by theabovediscussed patents.

It is contemplated by this invention to provide a method and apparatusfor measuring the volume of the test chamber of the meter prover with anaccuracy to one part in 10⁶. Once the volume can be obtained with suchaccuracy, then it is necessary to insure, as taught by this invention,that the structure containing the chamber is rigid and nondeformable. Inthe past, the bell-type enclosures have not provided such a rigidstructure so that if they were accidentally jarred, the interior volumemay be changed to a degree to affect the accuracy of the bell-type meterprover's readings. As will be disclosed, this invention adopts atechnique for measuring the displacement volume within the meterprover's chamber by generating electromagnetic waves and determining thefrequency at which resonance is established at first and secondpositions of a piston to be driven through the housing. Adopting such amethod of measuring the container's volume requires, as taught by thisinvention, the use of a housing having a substantially perfect rightcircular cylinder configuration so that the frequencies at whichresonance is established, may be determined sharply to thereby determinethe displacement volume within the rigid cylinder. Further, in thedevelopment of the invention to be described, it became evident thatonce the volume of the prover had been determined with great accuracy,then it was necessary to determine other parameters as would affect theindication of meter registration or of the volume of fluid as drawnthrough the meter under test, with similar accuracy. In this regard, theinvention contemplates methods and apparatus for measuring with a highdegree of accuracy the temperature an pressure of the fluid within themeter and within the meter prover such that a correction factor may bedetermined with a similar degree of accuracy to thereby correct forvariations in these parameters that exist in the meter under test andthe meter prover of this invention. Such a technique contrasts to theprior art, wherein a meter prover was put into an environmentallyconditioned room with limited variations in the temperature and pressureof that room. However, when the precision with which the variables areto be measured approaches 10⁶ as has been achieved by this invention forthe measurement of the displacement volume of the meter prover, then itbecomes necessary to note that these parameters of pressure andtemperature do vary within the meter prover and within the fluid flowmeter during the course of its test such that to insure desiredprecision, that new methods and apparatus for measuring pressure andtemperature must be provided. For example, if there is an error of 1° F.in the measurement of fluid temperature, there may result an error of0.2% in the displacement volume indicated by the prover. It iscontemplated that the meter prover system of this invention is capableof achieving an indication of the volume as drawn through the meterunder test to a precision of 0.004%. With such accuracy, theninvestigations may be conducted to determine the effects of otherfactors upon the measurement of fluid flow. For example, the number oftimes that tests are performed upon a given meter will affect themeasured meter registration. Further, it is contemplated that thevariation in the rate of fluid flow as well as the volume of fluid flowthrough the meter will affect the indicated measured volume by the meteras well as its meter registration with respect to its standard volume asmeasured by a meter prover.

BRIEF SUMMARY OF THE INVENTION

In accordance with this invention, there is disclosed apparatus andmethod of measuring the volume of a meter prover including a chamber,illustratively taking the form of a substantially perfect right circularcylinder, and a piston adapted for rectilinear movement within saidcylinder between a first position and a second position. The volumemeasuring apparatus comprises an antenna disposed within the chamber anda generator coupled to apply electromagnetic energy to the antennawhereby electromagnetic waves are emanated into the chamber. A detectoris coupled to the antenna to detect electromagnetic energy reflectedfrom the chamber and is in turn coupled to a resonant detector in theform of a cathode ray tube, wherein a minimum in the level of theelectromagnetic energy may be determined. Further, a frequency detectorin the form of a counter, is connected to the output of the generator todetect the frequencies of the generator output at which the minimumlevel occurs as observed upon a display device corresponding to theestablishment of a resonant standing wave within the chamber of themeter prover. The frequency(ies) at which the resonant standing wavesare established within the chamber, in turn determine the volume of themeter prover chamber. The electromagnetic field(s) are generated withinthe chamber of a mode selected so that at a resonant condition withinthe chamber, the electric and magnetic component fields of theelectromagnetic field have a defined relation to the dimensions of thechamber of regular geometry, illustratively, a right circular cylinder.

BRIEF DESCRIPTION OF THE DRAWINGS

A detailed description of one preferred embodiment of this invention ishereafter described with specific reference being made to the drawingsin which:

FIG. 1 is an elevational view of a meter prover system in accordancewith the teachings of this invention;

FIGS. 2A and B are detailed, partially sectioned views of the meterprover of this invention as more generally shown in FIG. 1,

FIG. 2C shows the structure for housing the meter prover as shown inFIGS. 1 and 2A and a control console whereby the operator may controland observe the data output from the meter prover, and

FIG. 2D shows the display panel of the system control and status moduleas shown in FIG. 2C;

FIG. 3 is a functional block diagram of the architecture of the computersystem used to sense the several variables of the meter prover systemand to control the movement of the piston through the cylinder of theprover as shown in FIGS. 1 and 2A, as well as to provide an accurateindication of the meter registration of the tested meter.

FIGS. 4A to 4E show the various signal conditioning and interfacecircuits as are needed to provide signals into and from the computersystem as shown in FIG. 3;

FIG. 4F shows a perspective view of the meter and the manner in which aproximity detector is disposed with regard to its encoder mechanism, and

FIGS. 4G through M show detailed schematic diagrams of the signalconditioning and interface circuits generally shown in FIGS. 4A and E;

FIG. 5 shows a high level diagram of the program as executed by thecomputer system of FIG. 3;

FIGS. 6A and 6B show in a more detailed diagram, the initializationprocess effected by the computer system of FIG. 3;

FIG. 7 shows in a more detailed fashion the steps necessary to calibratethe inputs as applied to the signal conditioning and interface circuitsfor applying the measurements of temperature and pressure to thecomputer system as shown in FIG. 3;

FIGS. 8A through 8P disclose in detail the flow diagram for reading outdata stored within the computer system and to enter the conditions underwhich the meter prover system will test a given meter (the letters I andO are not used for clarity sake);

FIGS. 9A to 9Q show the steps effected by the computer system of FIG. 3to carry out the various tasks and to provide manifestations thereof(the letters I and O are not used for clarity sake);

FIG. 10 is a schematic diagram of a circuit for applying a highfrequency signal to the microwave antenna within the cylinder of themeter prover as shown in FIGS. 1 and 2A, for varying the signal'sfrequency as applied to the antenna whereby the volume of the cylindermay be determined with great accuracy to thereby accurately encode theoutput of the meter prover's linear encoder;

FIGS. 11A through E show variously the input signals applied to and theoutput signal as developed by the signal conditioner and logic circuits170a and 170b as shown generally in FIG. 4C and more specifically inFIG. 4K;

FIGS. 12A and B show respectively a perspective view of a cover to beplaced over the piston as shown in FIGS. 1 and 2A, and a cross-sectionalview of the spring-like seal disposed about the periphery of the pistoncover;

FIG. 13 is a graph illustrating the response of a chamber of a rightcircular cylinder configuration to being excited with high frequencyelectromagnetic fields in terms of the varying dimensions of the cavityand frequencies of excitation; and

FIG. 14 is a cavity response curve showing reflected power Pr as afunction of the excitation frequency.

DETAILED DESCRIPTION OF INVENTION

Referring now to the drawings, and in particular to FIGS. 1 and 2A,there is shown the meter prover system 10 of this invention as coupledto a meter 38 to be tested. The meter prover system 10 includes acylinder 12 through which a piston 14 is driven in rectilinear fashion,by a programmable, variable speed motor 20 such as a servomotor.

The cylinder 12 is supported in upright position by a series of struts76 (only two of which are shown) secured to a collar 77 which in turn issecured around the exterior of cylinder 12. The upper end of cylinder 12is closed by a head 86 from which a series of struts 88 (only one ofwhich is shown) extend upwardly. A support plate 94 is fixed to theupper end of struts 88 and servomotor 20 is mounted on the top of plate94. The upper end of a lead screw 18 is journalled for rotation in plate94 by means of bearing 98 and is drive connected to the drive shaft ofthe servomotor 20 by means of a coupling 100. A lead nut 22 fixed withina housing 23 is threadedly received on lead screw 18. The lead screw 18is telescoped within sleeve 17, the upper end of which is secured to thehousing 23. The lower end of sleeve 17 projects through and is slidinglyreceived in bushing 96 in head 86. The upper end of piston shaft 16 issecured to the lower end of sleeve 17.

An intermediate cylinder head 91 separates the upper portion of theinterior of cylinder 12 from the lower portion in which the piston 14 iscontained. Piston shaft 16 projects through and is slidably received inbushing 93 in head 91, the lower end of shaft 16 being connected to thepiston 14.

Thus, as the servomotor 20 rotates, the lead screw 18 rotates in nut 22causing the housing 23, sleeve 17, and shaft 16 to move vertically ineither direction depending on the direction of servomotor rotation.

The bottom of cylinder 12 is closed by a head 60 and the cylinder 12therefore encloses and defines between the piston 14 and head 60 avariable volume chamber 28. An opening 62 in head 60 places chamber 28in communication with conduit 30, conduit 32, and meter 38. A firstinlet valve 34 is disposed between the cylinder 12 and the meter 38 tocontrol the flow of fluid, e.g., a gas, therebetween. A second, exitvalve 36 is connected to the conduit 30 in order to permit the exit offluid from the cylinder 12 when the valve 36 has been opened.

The precise position of the piston drive shaft 16 and therefore thepiston 14 is provided by a high precision, linear optical encoder 26that is coupled to the drive shaft 16 to move therewith. Morespecifically, the encoder 26 illustratively includes first and secondsets of light sources and photodetectors disposed on either side of alinear scale 24 having a high number of scale marks 102. In oneillustrative embodiment of this invention, the linear scale 24 isdisposed in a fixed position with respect to movable encoder 26 andincludes 40,000 scale marks 102 (2500 marks per inch); of course, only alimited number of such a high number of scale marks could be illustratedin the drawings. Thus, as the encoder 26 is moved rectilinearly alongthe length of the linear scale 24, first and second sets of pulse trainsA and A are developed, 90° out of phase with respect to each other, asthe light beams generated by the first and second light sources areintercepted by the scale marks 102. The outputs A and A from the opticalencoder 26 indicate precisely the position of the piston 14 and likewisethe volume of fluid has been drawn through the meter 38. As will beexplained, the volume of the chamber 28 within the cylinder 12 isprecisely measured, and each output pulse derived from the encoder 26provides a precise indication of an incremental volume as drawn into thechamber 28 within the cylinder 12 as the piston 14 is withdrawn, i.e.,is directed upward by the servomotor 20. Before the piston 14 is begunto be raised, thus creating a vacuum within the chamber 28 the exitvalve 36 is closed and the meter valve 34 is opened to permit a flow offluid through the meter 38 via the conduit 32, the open valve 34 and apair of conduits 30 and 32 into the housing 28. During a meter test, themeter 38 provides via its encoder 40 an output train of pulsesindicative of the flow of fluid therethrough. The train of pulses asderived from the meter encoder 40, is compared to the train of pulsesderived from the linear encoder 26 to provide an indication of the meteraccuracy in terms of the meter registration, a ratio corresponding tothe volume measured by the meter encoder 40 to the volume measured bythe linear encoder 26.

Further, the programmed movement of the piston 14 uses a plurality ofproximity sensors 50, 52, and 54, as well as a pair of limit switches 49and 53. As will be explained, the servomotor 20 drives the piston 14rectilinearly within the housing 28. As shown in FIGS. 1 and 2A, thepiston 14 is in its uppermost position wherein an abutment 92 on housing23 26, contacts and closes the upper limit switch 53 thereby deactuatingthe servomotor 20 when the piston 14 is driven upward and therebyhalting the movement of the piston 14. When the servomotor 20 drives thepiston in a downward direction as shown in FIG. 1, the abutment 92 maythen engage the lower limit switch 49 again bringing the piston to ahalt. The upper failsafe switch 53 and the lower failsafe switch 49 areused to prevent physical damage to the meter prover 10 if for reason offailure, the servomotor 20 should continue to drive the piston 14 toeither extremity. If the abutment 92 should engage either of thefailsafe switches 49 or 53, the servomotor 20 will be deenergized andthe piston brought to an abrupt halt. Also in a volume self-test mode ofoperation, as will be explained, the proximity detectors 52 and 54 areused to detect the movement of the piston 14 between designatedlocations. In general, the servomotor 20 accelerates the piston 14 to agiven speed and the output of the linear encoder 26 is gated by theoutput of the proximity detector 52 to permit its pulses to beaccumulated and counted. The counting of the pulses derived from thelinear encoder 26 is gated off, in the volume self-test mode, by theoccurrence of an output from the proximity detector 54 indicating thepassage of the abutment 92 there past. Thereafter, the servomotor 20 isdecelerated to a stop. By contrast, in the meter test mode, the piston14 is driven upward by the servomotor 20 and when the abutment 92 passesthe proximity detector 52, an enable signal is generated thereby wherebyon the occurrence of the next or leading edge of the next output pulsefrom the meter encoder 40, the counting of the output pulses of thelinear encoder may then begin. In the meter test mode, the counting ofthe linear encoder pulses is terminated when the counting of the meterencoder pulses has reached a predetermined count corresponding to avolume of fluid drawn through the meter.

In order to facilitate an understanding of this invention, a briefsummary of its operation will now be given, while a more detaileddiscussion of the operation of the meter prover 10 will be providedbelow. A first or initialization mode determines whether the piston 14is in its park position as by determining whether the proximity detector50 detects the presence of the abutment 92 as explained above; if notthe servomotor 20 is energized to drive the piston 14 to its parkposition. If the abutment 92 is in a position to be detected or beforethe piston 14 is returned to its park position, the second or exit valve36 is opened to permit the exit of fluid driven from the chamber 28through the conduit 30, and then the inlet meter valve 34 is closed toprevent the fluid from being driven therethrough and possibly injuringthe meter 38. Upon command of the operator that a meter 38 is to betested, first meter valve 34 is opened and then the second valve 36 isclosed to permit the flow of fluid through the meter 38, the conduit 32,the open valve 34 and the conduit 30 into the chamber 28, as the piston14 is being driven in an upward direction by the servomotor 20. Thepiston 14 is gradually accelerated to a given steady state volocity andis maintained at that selected velocity during the course of the fluidvolume test measurement, while the output pulses of the encoders 26 and40 are accumulated by an arithmetic unit including registers toaccumulate counts indicative of a precise volume as measured by thelinear encoder 26 and of the volume as measured by the meter 38,respectively. The meter test is initiated by the passage of the piston14 past the start-test proximity detector 52 that enables upon theoccurrence of the next output pulse or more precisely its leading edgefrom the meter encoder 40, the counting or accumulation of the meterencoder pulses as well as the linear encoder pulses. Dependent upom thedesired volume to be drawn through the meter 38 under test, the metertest will terminate upon the counting of a number of meter encoderpulses. In particular, the register for accumulating the meter encoderpulses 38 upon counting the predetermined number dependent upon thefluid volume, provides an output applied to the linear encoder systemterminating its counting of the input pulses derived from the meterencoder 40. The stored counts indicative of the fluid volume as measuredby the meter encoder 40 and the linear encoder 26 are compared, i.e., aratio therebetween is obtained to provide an indication of the meterregistration.

In addition, measurements of temperature and pressure are taken in orderthat the measured volumes may be adjusted for these conditions. Inparticular a pair of temperature measuring devices 42 and 44 arerespectively disposed at the entrance and exit ports of the meter 38. Adifferential pressure transducer 46 is disposed to measure thedifference between the pressure established by the fluid in the conduit32 and ambient pressure. In addition, temperature measuring devices 48and 57 are disposed respectively at the conduit 30 coupled to thechamber 28 and upon the piston 14 to provide indications of thetemperature of the fluid within the chamber 28. In addition, a seconddifferential pressure transducer 51 is disposed within the piston 14 toprovide an indication of the differential pressure between the ambientpressure and that established within the chamber 28. The temperatureoutputs TM3 and TM4 derived from the temperature measuring devices 42and 44, respectively, are averaged to provide an average metertemperature AMT, whereas the outputs TP1 and TP2 of the temperaturemeasuring devices 57 and 48, respectively, are averaged to provide anindication of the average prover temperature APT. As will be explainedin greater detail later, these input parameters are used to provide anadjustment of the measured volumes as derived from encoders 26 and 40dependent upon the measured conditions of pressure and temperature.

As shown in FIG. 2A, a microwave antenna 70 is disposed in the head 60to generate microwaves within the chamber 28, whereby its volume may beaccurately determined. It is contemplated that this measurement may bemade periodically to detect even the minutest changes in the volume ofthe chamber 28. As will be explained, the techniques of establishingelectromagnetic waves in the microwave range permits an accuracy to atleast one part in 10⁶ of the volume of the chamber 28. In addition, inorder to test the accuracy of the temperature sensors 48 and 57, a highprecision temperature measuring device 68 is also inserted within theconduit 30. The temperature transducers 48 and 57 may illustrativelytake the form of a RTD Model No. 601222 temperature transducer asmanufactured by Senso-Metrics, Incorporated, whereas the high precisiontemperature transducer 68 may be of the type as manufactured by HewlettPackard under their Model No. 18115A; this transducer 68 must be usedwith a Hewlett Packard 2804A quartz thermometer. The proximity switches50, 52, and 54 may illustratively take the form of a proximity switch asmanufactured by Microswitch under their designation FMSA5, whereas thelimit switches 49 and 53 may be of a type as manufactured by Microswitchunder their designations BA-2R-A2 and ADA3721R. The servomotor 20 mayillustratively take the form of that manufactured by Control SystemsResearch, Inc. under their designation NC100DC Servo Motor/Tachometer.The optical encoder 26 and scale 24 may take the form of a Pos-Econ-5linear encoder as manufactured by Heindenhain Corporation. As will beexplained later in detail, the measurements of pressure and temperaturewithin the meter 38 and within the prover 10 are used to calculate afactor by which the volume as drawn into the prover 10 is adjusted forthese variables. In particular, the temperature transducers 48 and 57measure the temperature at the bottom and topmost portions of thechamber 28 to obtain a spatially averaged measurement of the temperatureacross the entire volume within the chamber 28 of the prover 10. Insimilar fashion, the temperature transducers 42 and 44 provideindications of the temperatures of the gas at the inlet and outlet ofthe meter 38 whereby a spatial averaging of the temperature of the gasflowing through the meter 38 may be obtained. The temperaturetransducers as selectively incorporated into the meter prover 10 arehighly stable, low-thermal-mass platinum resistance thermometers andprovide accurate readings of these variables whereby the volume as drawninto the meter prover 10 may be accurately determined.

As shown in FIGS. 2A and B, the proximity devices 50, 52, and 54, aswell as the limit switches 49 and 53 are supported upon the uprightmember 90, which is in turn supported from one of the upstanding struts88. One end of the linear scale 24 is supported from the member 94 andextends downward substantially parallel to the direction of the movementof the piston 14, having its lower end supported upon an upper portionof the interior of the cylinder 12. Only a limited number of the some40,000 markings 102 are shown in FIG. 2A. In the lowermost portion ofFIG. 2A, the inlet valve 34 and the exit valve 36 are actuated,respectively, from open to closed positions by pneumatic actuators 66and 64, respectively.

In FIG. 2A, there is shown a sealing means indicated generally at 78 forthe piston 14 to prevent the fluid as drawn through the meter 38 andinto chamber 28 from leaking about the edges of the piston 14 as it ismoved rectilinearly within the cylinder 12. The details of this pistonseal 78 are disclosed in the U.S. patent application entitled "PistonSeal", filed concurrently herewith and assigned to the assignee hereof.

Referring now to FIG. 2C, the meter prover 10 is shown as being disposedwithin a controlled environment formed by an enclosure 104 comprising aprover room 106 for receiving the meter prover 10 and a control room105, wherein the control's console is disposed and includes a displayunit 111 containing a printer and a series of lights for indicating thevarious states of the meter prover, a CRT terminal 112 including akeyboard whereby various commands may be input by the operator, and avariety of heat generating equipment including power supplies, motorcontrol, amplifiers, etc. The control of the ambient conditions aboutthe meter prover 10 is insured by disposing the meter prover 10 withinthe prover room 106 remote from the heat generating display unit 111 andterminal 112. As shown in FIG. 2C, the meter 38 to be tested is alsodisposed within the prover room 106 and is coupled to the meter prover10 by the conduit 32. The temperature in the prover room 106 is measuredby the four temperature sensitive devices R0, R1, R2, and R3 disposedabout the prover room 106 and upon a strut 76 of the prover 10. Abarometric pressure transducer 109 and a barometer are also disposedwithin the prover room 106 to measure the ambient pressure. Electricalconnections are made to the various temperature measuring devices asshown in FIG. 2C, as well as those temperature and pressure measuringdevices as shown in FIGS. 1 and 2A and are directed through a pair oftroughs 110 to the control console disposed within the control room 105.In this manner, the ambient conditions under which the meter 38 to betested and the meter prover 10 operate can be accurately controlled toinsure the integrity of the measurements being made upon the meter 38and the meter prover 10.

Referring now to FIG. 3, there is shown a functional block diagram ofthe computer architecture of the computer system implementing thevarious functions including processing of the temperature and pressuremeasurements, of the linear encoder and meter encoder output signals,and to appropriately close the valves 34 and 36. In addition, outputsare provided to the CRT terminal 112 to indicate the measured parametersas well as to the system control and the display unit 111 to display thevarious states of operation of the meter prover system 10, whilepermitting operator input through the keyboard of the CRT terminal 112,of selected meter test functions. The computer system includes a centralprocessing unit (CPU) 120 of the type manufactured by the assignee ofthis invention under their designation PPS-8 Microcomputer, from whichaddress signals are applied from CPU 120 via an address bus 128 to aprogrammable read only memory (PROM) 124 and to a random access memory(RAM) 126. The RAM 126 may take the form of the 256×8 RAM asmanufactured by the assignee of this invention, whereas the PROM 124 maytake the form of that PROM manufactured by Intel Corporation under theirdesignation 2708. A system clock 122 provides system clock signals(e.g., 200 KHz) to the CPU 120 and may illustratively take the form ofthe clock generator circuit P/N 10706 as manufactured by the assignee ofthis invention. As shown in FIG. 3, each of the clock 122, the CPU 120,the PROM 124, and the RAM 126 are interconnected by an instruction-data(I/D) bus 140, which may illustratively take the form of a 14-line busnot only interconnecting the forementioned elements but also connectedto each of the signal conditioning and interface circuits 130, 132, 134,136, and 138.

The circuit 130 conditions and interface the signals indicative of theprover temperature signals TP1 and TP2 as derived respectively from thetemperature measuring devices 57 and 48. Further, the meter temperaturesignals TM3 and TM4 as derived from the devices 42 and 44 are alsoapplied to the circuit 130. As shown in FIG. 2C, four additional roomtemperature measuring devices R0, R1, R2, and R3 are provided about theprover room 106 in which the meter prover system 10 as shown in FIGS. 1and 2A is disposed; in this regard it is understood that the ambientconditions about the meter prover system 10 are well regulated in orderto maintain stable as possible the ambient temperature of the meterprover system 10. It is normal practice to store the meters 38 to betested in this environment for a time to permit them to reach the sameambient conditions at which the meter prover system 10 is disposed. Asshown in FIG. 3, the temperature signals are applied to a signalconditioner and logic circuit 150 and from there via an interfacecircuit 151 to the I/D bus 140.

In similar fashion, the pressure signals are applied to the conditioningand interface circuit 132, which comprise a signal conditioner and logiccircuit 162 and an interface circuit 164. In particular the outputs ofthe differential pressure measuring device 51 indicating thedifferential pressure PP1 of the prover 10 and of the differentialpressure measuring device 46 indicating the meter pressure MP2, and thebarometric pressure measuring device 109 indicating the ambient oratmospheric pressure PB of the prover room 106 are applied to thecircuit 132.

The output of the meter encoder 40 and the linear optical encoder 26 areapplied to the signal conditioning and interface circuit 134. Inparticular, the output of the meter encoder 40 is applied to a signalconditioning and logic circuit 170a, whose outputs are applied in turnto interface circuits 171 and 173. A clock circuit 175 applies a signalto the interface circuit 173. In an alternative embodiment of thisinvention, a proximity detector 27 is used for detecting the rotation ofthe meter encoder 40 and the output of the proximity detector 27 isapplied to the signal conditioner and logic circuit 170a. This isillustrated in FIG. 3 by the input signals designated as rotary encoderpulses and meter test proximity detector; it is understood that only oneof these inputs is made at a time to the circuit 170a. The output of thelinear optical encoder 26 is applied via the signal conditioning andlogic circuit 170b and interface 179 to the I/D bus 140.

In order to provide an indication of the measured parameters, such astemperature, pressure, as well as the fluid volumes drawn by the prover10 and as measured by the meter 38, outputs are applied from the I/D bus140 via the circuit 136 to the display unit 111 which includes a hardcopy data printer as manufactured by Practical Automation, Inc. undertheir designation No. DMTP-3. In particular, the circuit 136 includes aninterface circuit 192a for applying parameter output signals via asignal conditioner and logic circuit 190a to the hard copy printer.Further, the circuit 136 includes an interface circuit 192b providingthe parameter output signals via a signal conditioner and logic circuit190b to the CRT data terminal 112. In addition, operator input commandsignals as input on the terminal's keyboard are transferred via logiccircuit 190b and the interface circuit 192b to the I/D bus 140. A clockcircuit 193 controls the baud rate at which signals may be transferredbetween the CRT data terminal 112 and the computer system. The CRT dataterminal 112 may illustratively take the form of a CRT display asmanufactured by Hazeltine Corporation under their designation 1500. Sucha terminal permits input commands via the alphanumeric keys upon itskeyboard, as well as to display the commands being entered, and theoperator accessed parametric data.

Finally, there is shown a signal conditioning and interface circuit 138for interconnecting the I/D bus 140 and the inlet valve 34 and theexhaust valve 36, as well as to apply the control signals to theservomotor 20. In addition, the servomotor 20 is associated with a motorcontrol such as the DC Servocontroller as manufactured by ControlSystems Research, Inc. under their designation NC101 whereby feedbacksignals indicative of the speed of the servomotor 20 are applied via thelogic circuit 194 to in turn affect the servomotor 20 control. Inaddition, signals indicating the status of the servomotor 20 as well asan input signal from a test mode switch to indicate whether the rotaryencoder 40 or proximity detector 27 are to be used to measure meterflow, is entered via the logic circuit 198 and the interface circuit 200to the I/D bus 140.

The signal conditioning and interface circuit 130 is shown in moredetail in FIG. 4A, as including two line inputs derived from each of thetemperature transducers 57, 48, 42, and 44 indicative respectively ofthe prover temperatures TP1 and TP2, and the meter temperatures TM3 andTM4, and is connected to a multiplexer 149. In addition, the fourtemperature transducers R0, R1, R2, and R3 disposed about the proverroom 106 in which the meter prover system 10 is housed, are appliedthrough the next four inputs to the multiplexer 149. The aforementionedtemperature transducers are connected into amplifier modules that serveto develop voltage outputs proportional to the temperature sensed and toapply these outputs to the corresponding inputs of the multiplexer 149.In this manner, each temperature transducer is associated with its ownamplifier module so that its output to the multiplexer 149 may beadjusted to insure a substantially uniform output in terms of voltageamplitude and off-set for each of the temperature transducers connectedto the multiplexer 149. The details of the amplifier modules for each ofthe transducers shown in FIG. 4A will be explained below with respect toFIG. 4I along with a detailed description of the signal conditioning andlogic circuit 150 as generally shown in FIG. 4A. The multiplexer 149serves to time multiplex the inputs at each of its eight inputs and toscale the temperature signal outputs to be applied one at a time via amultiplexer 154 to an amplifier 152 taking the illustrative form of thatamplifier as manufactured by Analog Devices under their designationAD522. The second multiplexer 154 is normally set to apply one of theeight temperature input signals via the operational amplifier 152 to theanalog digital (A/D) converter circuit 158, which may illustrativelytake the form of the A/D converter as manufactured by Burr Brown undertheir designation ADC 80. In a calibrate mode, the multiplexer 154 isactuated to apply a precision, calibrating voltage to the A/D converter158. As is well known in the art, the DC voltage of the analog signalsis adjusted to a level which may be readily accepted by the A/Dconverter 158, which in turn converts these analog signals to digitaloutputs which are applied via its 12 output lines to a parallelinput-output (PI/O) device 160 which may illustratively take the form ofthat device manufactured by the assignee of this invention under theirdesignation P/N 11696. The PI/O circuit 160 permits input commands to betransferred via the I/D bus 140 to the multiplexer 149 to control whichof the inputs is to be sampled at a particular time, as well as to thelogic circuit 156 to enable the multiplexer 154 to apply one of theoutputs of the multiplexer 149 or the voltage calibration input signalto the A/D converter circuit 158. In operation, the CPU 120 places acall signal via the I/D bus 140 to the PI/O circuit 160 which respondsthereto by enabling a call for information to be read out and convertedto digital data to be applied to the I/D bus 140. In addition, a commandis derived from the PI/O circuit 160 to time the conversion of theanalog signals to digital signals by the A/D converter circuit 158, anda signal indicative of the status of the A/D converter circuit isapplied via the PI/O circuit 160 to the I/D bus 140. The voltagecalibration signal permits the zero and span of the operationalamplifier 152 to be adjusted so that the full amplitude of each inputsignal may appear at the A/D converter circuit 158.

The conditioning and interface circuit 132 is more fully shown withrespect to FIG. 4B wherein there is shown that the outputs of thetransducer 51 and 46 indicating respectively the prover or pistonpressure PP1 and the meter pressure MP2 are applied via operationalamplifiers 161a and 161b to a multiplexer 163. In addition, the outputfrom the pressure transducer 109 for measuring the barometric or ambientpressure of the prover room 106 is applied via operational amplifier161c to the multiplexer 163. Initially, the CPU 120 transmits a commandto the multiplexer 163 to select which of the outputs of the pressuretransducers 51, 46 or 109 is to be read out via the I/D bus 140 and theparallel input-output (PI/O) circuit 168. In response thereto, the PI/Ocircuit 168 applies control signals via the four-line bus 169 to themultiplexer 163, to select one of the three pressure indicating signalsor a signal indicative of the voltage calibration input signal to beapplied to an A/D converter 166, which converts the input analog signalto a corresponding digital signal to be applied to the PI/O circuit 168to be in turn transmitted via the I/D bus 140. Next, upon command of theCPU 120, the PI/O circuit 168 commands via line 159 the A/D circuit 166to convert the selected analog pressure output signal to a correspondingdigital signal to be transmitted via the I/D bus 140. The conversion ofthe input analog data to digital data requires a discrete time periodfor the A to D conversion to take place and in addition, for the digitaldata appearing upon the 12 output data lines of the A/D circuit 166 tostabilize before they are read by the PI/O circuit 168. When signalstabilization has occurred on the 12 data lines output from the A/Dcircuit 166, a status signal is generated by the A/D circuit 166. Inresponse to the status signal, the PI/O circuit 168 reads the dataappearing on the output lines of the A/D circuit 166 and applies thesesignals via the I/D bus 140 to the RAM 126 as shown in FIG. 3. Afterthis process is completed, the system is able to select another pressureoutput as derived from another transducer, converting same to a digitalsignal to be transmitted to the RAM 126 as explained above.

The interface and conditioning circuit 134 is more fully explained withrespect to FIG. 4C. The rotary meter encoder 40 is coupled to the meter38 to provide first and second signals A and A, 90° out of phase witheach other, to the signal conditioning and logic circuit 170a. Inparticular, the circuit 170a processes the input signals A to A toeliminate possible problems due to jitter of the signals as may beimposed by mechanical vibration upon the rotary meter encoder 40. Thesignal conditioner and logic circuit 170a generates a composite pulsesignal corresponding to each set of input pulses of the signals A and A,and applies same to an interval timer 174 including a programmablecounter 174a into which is loaded a factor dependent upon the selectedvolume of fluid to be drawn through the meter 38, in a manner that willbe explained. In particular that factor is placed in the programmablecounter 174a and upon counting down to zero from that factor, a pulse isgenerated by the interval timer 174 and applied to a logic circuit 177whose output is applied to initiate a CPU Interrupt 2 subroutine,whereby the testing of the meter 38 is terminated, as will be explainedlater in detail with respect to FIG. 9J. The logic circuit 170a isresponsive to the input signal A from the rotary meter encoder 40 toapply a corresponding, conditioned pulse to an interval timer 176, whichperforms the operation of recognizing the leading edge of the signal Ato initiate timing or counting of the programmable counter 174a as wellas of the counter 176a and of the linear encoder counter 182. Morespecifically, the CPU 120 controls the meter prover 10 and senses thatthe piston 14 has been accelerated from its park position to itsstart-test position, as indicated by the presence of an output signalfrom the proximity detector 52. Upon the sensing of the output ofproximity detector 52, the program as executed by the CPU 120periodically, e.g., approximately every 40 microseconds, accesses theinterval timer 176 to see whether it has received an input signal fromthe signal conditioner and logic circuit 170a indicative of the leadingedge of the input signal A of the rotary encoder transducer 40. Upon thedetection of the first leading edge of the output of the logic circuit170a, after the piston 14 has passed the proximity detector 52, aninitiate signal is applied to the PI/O circuit 184, which applies aninitiate count signal to the counter 182 and also an initiate signal viathe I/D bus 140 to the programmable counter 174a. In this manner, eachof the counters 174a, 176a, and 182 are activated to start counting atthe same time. In this illustrative example, the programmable counter174a counts down in response to output signals of the rotary encodertransducer 40.

In a significant aspect of this invention, the initiating andterminating of the meter test, i.e., the counting by the programmablecounter 174a and the counter 182, are made responsive to the output ofthe rotary encoder 40 in that the accuracy of the meter 38 is to bemeasured. More specifically, the rotary encoder 40 is coupled to thefluid or gas meter 38 as will be more fully described with respect toFIG. 4F and upon rotation of its rotatively mounted rod, the rotarymeter encoder 40 as coupled thereto will produce a train of pulsescorresponding to the rotation this tangent arm and the cycling of themeter's diaphragm. As shown in FIG. 4F, the rotary member is connectedby coupling arms to the meter diaphragm and its rotation is not linearso that the output of the encoder 40 is in a sense frequency modulated.Therefore, in order to obtain an accurate measurement of the rotarymeter encoder 40, it is desired to count the pulses as derived from theencoder 40 so that the counting begins and terminates at approximatelythe same point in the rotation of the meter's rotary member. This isaccomplished by initiating the counting in response to the rotary meterencoder 40. In particular, a meter test is conducted by accelerating thepiston 14 from its park position to a steady state velocity so that uponits passing the proximity detector 52, disposed at the start-testposition, an output is provided therefrom to enable, as will beexplained later, the detection of the leading edge of the next outputsignal from the logic circuit 170a corresponding to the leading edge ofthe next output signal A of the rotary meter encoder 40. The intervaltimer 176 responds to the leading edge to effect the simultaneousinitiation of the counting of the programmable counter 174a and thecounter 182. Upon the occurrence of the programmable counter 174a beingcounted down from its selected factor dependent upon the desired volumeto be drawn through the meter 38, the interval timer 174 provides itsoutput to the logic circuit 177 to enable Interrupt 2 of the CPU 120,which in turn terminates the counting of the counters 174a and 182 andtransfers the respective counts to corresponding locations within theRAM 126. It is noted that the termination of counting could beimplemented by software, but would involve an additional number of stepsthus unduly complicating the programming of this system as well asadding to the time required to carry out the timing operation asdescribed above. In addition, the effecting of the initiating ofcounting in response to the output of the rotary meter encoder 40insures a more accurate test and calibration of the meter 38 under test.

As explained above, the output train of pulses as derived from therotary encoder 40 is applied to count down the count initially placed inthe programmable counter 174a. Significantly, the count as placed in theprogrammable counter 174a is variable dependent upon the volume desiredto be drawn through the meter 38 and into the chamber 28. The count isbased upon the structural dimensions of and characteristics of the meter38, as well as the characteristics of the rotary meter encoder 40 interms of the number of pulses it generates per revolution. In anillustrative embodiment of this invention, a count of 40,000 is placedin the programmable counter 174a corresponding to a volume of one cubicfoot to be drawn through the meter 40. Assuming that the characteristicsof the meter 38 and the encoder 40 remain the same for varying volumes,illustrative counts of 20,000 and 10,000 may be stored in theprogrammable counter 174a if it is desired, respectively, to drawone-half and one-fourth cubic foot of fluid through the meter 38. Byentering a count based upon the characteristics of the meter 38 into thethe programmable counter 174a which is counted down by pulses derivedfrom the rotary meter encoder 40, a more accurate test of the meter isassured in that the beginning and ending of meter test will be effectedat the same point in the cycle of the rotation of the meter and itsrotary encoder 40, as explained above.

As indicated in FIG. 4C, a clock A is derived from the system clock 122via the CPU 120 and the I/D bus 140 is applied to the interval timer176. A selected factor is placed into down counter 176a to provide anoutput from the interval timer 176 corresponding to a sampling pulse ofone pulse per second. In an illustrative embodiment of this invention,the system clock as derived from the clock 122 is in the order of 200KHz, and the factor placed in the counter 176a is such to provide thedesired one pulse per second to the logic circuit 178 and therefrom tothe motor control board. As will be explained later, this sampling pulseis used to time the sampling of the measurements of pressure andtemperature.

Further, the output of the linear encoder 26 is a pair of signals A andA, 90° out of phase with each other, which are applied to a signal andconditioner circuit 170b. The circuit 170b is similar to circuit 170a inthat it processes the inputted signal A and A to shape and conditionthese input signals eliminating jitter that might otherwise indicate afalse output from the linear encoder 26. In addition, the circuit 170bis able to detect the direction in which the piston 14 is moving fromthe inputted signals A and A and if the outputted signals A and A do notindicate that the piston 14 is moving in the desired direction, nosignals are outputted from the signal and conditioner circuit 170b. Thecircuit 170b provides a train of conditioned pulses corresponding to thelinear encoder output to the counter 182, which after initiation countsand accumulates the output of linear encoder 26. The accumulated outputof the counter 182 is applied to PI/O circuit 184 and upon command istransferred via the I/D bus 140 to the remaining portions of thecomputer system.

In one embodiment of this invention, a rotary encoder transducer 40 iscoupled to the meter 38 and in particular includes an optical encoderrotatively coupled to the domestic meter tangent arm of the meter 38 todetect the rotation of the tangent arm as gas flows therethrough toprovide a plurality of output signals A and A as explained above. In analternative embodiment of this invention, the proximity detector 27 maybe used to detect the mechanical rotation of the domestic meter tangentof the meter 38 by a mechanism that will be explained later to providean output signal to a signal conditioner and logic circuit 170c, whichis in turn connected to the interval timer 176 and to the interval timer174. Due to the arrangement of the mechanical mechanism coupled to thetangent arm of the meter 38, the proximity detector 27 produces a signalof lesser resolution than that produced by the optical encoder 26, as itdetects the rotation of the meter tangent arm; the particular advantageof the proximity detector arrangement is that of the relative simplicityof its mechanical and electrical structure. The choice of whether to usethe proximity detector 27 or the rotary encoder transducer 40 is made bythe operator by throwing a switch 191, as shown in FIG. 4K. When theoperator determines to use the proximity detector 27, the programmablecounter 174a is encoded with numbers of 8, 4, and 2 corresponding tomeasured volume flows of one cubic foot, one-half cubic foot, andone-fourth cubic foot. The operator initiates the entering of theappropriate factors whether for the proximity detector 27 or for therotary encoder 40, by first throwing the switch 191 to the appropriateposition and entering the test volume via the keyboard of the CRTterminal 112.

In FIG. 4F, there is shown a perspective view of a typical meter 38,which measures the fluid flow by the use of two diaphragms, only one ofwhich is shown as 1202; the flow meter as shown in FIG. 4F is more fullyexplained in U.S. Pat. No. 2,544,665 dated March 31, 1951. As shown, aflag rod 1203 senses the flexing of the diaphragm 1202 to cause the arm1204 to oscillate. A second diaphragm (not shown) and an associated flagrod (not shown) cause arm 1206 to oscillate in an alternate cycle. Asexplained in the noted patent, the combination of the arms 1206 and1204, and the arms 1208 and 1210 cause the tangent arm 1214 to rotate asdescribed in said patent. A metallic target 1212 at the point ofintersection of the arms 1208 and 1210, is rotated past the proximitydetector 27, whereby an output is provided to the logic circuit 170c tobe processed as explained above.

The conditioning and interface circuit 136 is more fully shown withrespect to 4D, wherein communication is made between the printer 111a,the display unit 111 for printing out desired parameters as measured bythe meter prover system 10 including the measured flow rate(s) and thepercentage(s) of error for the tests performed. In particular, theprinter 111a is coupled to the I/D bus 140 via a first logic circuit190b, and a parallel data controller (PDC) 192b, which mayillustratively take the form of the PDC as manufactured by the assigneeof this invention under their designation number 10453 and provides atwo-way controlled access between the I/D bus 140 and the printer 111a.Thus, on command through the PDC 192b, a signal is developed by thelogic circuit 190b whereby the printer 111a is strobed and anappropriate acknowledging signal (ACKO) is transferred via the logiccircuit 190b and the PDC 192b to indicate that the printer 111a isavailable for printing. If the printer 111a is busy, an appropriate busysignal will be transmitted back to the I/D bus 140. If a command hasbeen issued to print data, the control portion of the signal istransmitted via the PDC 192b and the logic circuit 190b to control theprinter 111a to print that data which appears upon the data channelderived from the logic circuit 190b.

Further, the operator may enter appropriate commands upon the keyboardof the CRT terminal 112 that is interconnected via the logic circuit190a and a serial data controller (SDC) 192a to the computer system viathe I/D bus 140. The SDC 192a may illustratively take the form of thatSDC as manufactured by the assignee of this invention under their modelNo. 10930. The SDC 192a is capable of receiving the serially orienteddata as derived from the CRT terminal 112 including instructions enteredby the operator upon the terminal's keyboard. The SDC 192a convertsthese serial signals inputted from the logic circuit 190a at anappropriate baud rate set by the clock 193, and transmits a set ofdigital signals via the I/D bus 140 to the CPU 120. In turn, data to bedisplayed upon the CRT terminal 112 is transmitted by the I/D bus 140via the SDC 192a and by the logic circuit 190a to be displayed upon theterminal's CRT.

The signal conditioning and interface circuit 138, as shown in FIG. 4E,interfaces between the I/D bus 140 and the first or inlet valve 34 andthe second or exhaust valve 36, as well as to provide signals to andfrom the motor control. Motor control signals in terms of speed anddirection are applied via the I/D bus 140 to be received and transmittedvia the PI/O circuit 196 to a logic circuit 194a whereby these digitalsignals are applied to the motor control to effect a correspondingaction of the servomotor 20. Similarly, at the appropriate time underthe control of the executed program, signals are developed to close orto open the valves 34 and 36 by actuating their corresponding solenoids66 and 64, respectively; these valve control signals are applied via thePI/O circuit 196 and the logic circuit 194b to a pair of pneumaticvalves disposed within the control room 105 as seen in FIG. 2C, wherebya 50 psi supply of air is selectively applied to each of the valvesolenoids 66 and 64, respectively, to open and close these valves uponcommand. In this manner, the heat generated by the valve solenoids isremoved from the temperature controlled prover room 106. In addition,each of the solenoids 66 and 64 includes a proximity detector todetermine whether the valve is open or closed. The output signalsdeveloped by the proximity detectors 50, 52, and 54 to determine theapproximate position of the piston 14 are applied via a logic circuit194c and the PI/O 196 to the I/D bus 140. A one second sampling clock isdeveloped from the encoder board (as explained above) and is applied viathe logic circuit 194d to the PI/O circuit 196. Similarly, the operatormay actuate a switch to determine whether the meter fluid flow is to beobtained from the proximity detector 27 or from the encoder 26, as shownin FIG. 4C; this command signal is applied via the PI/O circuit 196 tothe I/D bus 140. In order to achieve proper control over the servomotor20, the motor status in terms of its speed, direction, and measuredtorque is applied via the logic circuit 198b and the PI/O circuit 200 tothe I/D bus 140.

The display unit 111 includes a front panel as shown in FIG. 2D and isprovided to display a series of lights and backlighted pushbuttonsvariously indicating the condition of the system. As shown in FIG. 2D,the display panel includes the printer 111a for providing printouts ofthe flow rate and the percentage of the fluid through the meter 38. Inaddition, there is included a plurality of lights 111b to 111e. Thelight 111b is energized to indicate that a self-test of the meter prover10 is being run, as will be explained. The standby light 111e indicatesthat power has been applied to the meter prover 10 and that aninitialization process has been started to place the prover 10 in itsstandby mode. While in this standby mode, a series of keyboard responsesare required of the operator and upon completion of entry of the datavia the keyboard of the CRT terminal 112, the meter prover 10 willautomatically go into the test in progress mode as indicated by theenergization of the test in progress light 111c; in this mode, the meter38 is actually being tested. Upon completion of a meter test, the testcompleted indicator light 111d is energized. At this time, the finalpercent accuracy is calculated and is printed out on the hard copyprinter 111a. In addition, there is included a backlit stop pushbutton111g and a backlit reset pushbutton 111f. If during any phase of theoperation, the restart pushbutton 111f is depressed, the meter prover 10will respond as if power is initially applied, as will be more fullyexplained with respect to FIG. 9H. The stop pushbutton 111g is depressedonly when an emergency situation occurs that may cause damage to theprover 10. Upon depressing the stop pushbutton 111g, the servomotor 20is quickly decelerated to a halt and the prover 10 is locked up in itsstop mode until primary power is removed and reapplied. Uponreapplication of power, the meter prover 10 will return to the standbymode. During the course of the execution of the program, appropriatesignals are generated and applied via the I/D bus 140, the PI/O circuit200, and the logic and driver circuit 198a to energize the appropriateindicator lights 111b and 111e.

The signal conditioning circuits as shown in the functional blockdiagrams of FIGS. 4A to 4E are shown in more detail in the schematicdiagrams of FIGS. 4G to M. The signal conditioning circuit 130 asgenerally shown in FIG. 4A is more specifically shown in the schematicdiagrams of FIGS. 4G, 4H, and 4I.

In FIG. 4G, there is shown the multiplexer 149 as comprising a pluralityof relays having mercury wetted relay contacts, which reduce resistancepresented thereby and are coupled to the channels connected to theamplifier modules for providing to its relay of the multiplexer 149, avoltage corresponding to the temperature as measured by one of theprover temperature transducers 57 or 48, the meter temperaturetransducers 44 or 42, or one of the room temperature transducers R0 toR3. A selected channel is applied by the energized relay of themultiplexer 149 via the second multiplexer 154, as shown in FIG. 4G, andthe amplifier 152 to the A/D converter 158, as shown in FIG. 4H. In FIG.4H, there is shown the PI/O circuit 160 as being coupled by the I/D bus140 to the CPU 120. In addition, an output is derived from the PI/Ocircuit 160 to be applied to a HEX to one decoder 153, as shown in FIG.4G, which in turn energizes one of a plurality of drivers 155 to closethe corresponding relay of the multiplexer 149; the PI/O circuit outputis also applied via the logic circuit 156 as comprised of an AND gate156a, an inverter 156b, and a logic translator 156c to the multiplexer154. Further, with respect to FIG. 4H, when the output of a selected oneof the temperature measuring modules applied to the A/D converter 158, aconvert signal is applied to the A/D converter 158 from the PI/O circuit160 via the expander circuit 153. In response to this convert signal,the A/D converter 158 converts the inputted analog temperature signal toa corresponding digital signal to be transmitted via the PI/O circuit160 to the I/D bus 140, and transmits an end of conversion status signalvia the conductor 147 to the PI/O 160.

Referring now to FIG. 4I, there is shown a schematic diagram of anamplifier module to which each of the temperature measuring devices maybe applied and amplified to provide a voltage output signal to beapplied via a corresponding channel to the multiplexer 149.Illustratively, the temperature measuring devices may comprise aresistance temperature device as manufactured by Senso-Metrics undertheir designation No. 601222. The resistance temperature device (RTD) iscoupled as one arm of a resistance bridge 201 comprised of the RTD, andresistors R1, R2, and R3. The excitation voltage, as applied to the aand b terminals of the bridge 201, as well as the output voltage asderived from the terminals c and d thereof are coupled to a conditioningcircuit 203 as illustratively made by Analog Devices under theirdesignation Model 2B31. Basically, the conditioning circuit 203 includesan operational amplifier 205 to which is applied the output of thebridge 201 to be amplified before being applied to a Bessel filter 207whereby selected frequencies may be removed before being furtheramplified by an operational amplifier 209 to be applied to acorresponding channel of the multiplexer 149. An extremely stablevoltage supply serves to energize the circuit 203 and may illustrativelycomprise a voltage supply as manufactured by Analog Devices under theirdesignation AD584. As indicated in FIG. 4I, the gain of the operationalamplifier 205 is controlled by the resistance placed between terminals10 and 11 of the circuit 203, while the output offset is adjusted bysetting the potentiometer coupled to the terminal 29 of the circuit 203.In addition, the voltage and current as applied to energize the bridge201 are respectively controlled by adjusting the potentiometers R7 andR6.

The signal conditioning circuit 164 as generally shown in FIG. 4B isshown in more detail by the schematic diagram of FIG. 4J. The PI/Ocircuit 168 is shown as being coupled to the I/D bus 140 and to the CPU120 to provide transmission of data therebetween. A further input ismade from the A/D converter 166 via corresponding set of inverters 167to the PI/O circuit 168. The pressure transducers 51, 46, and PB areconnected respectively via the amplifiers 161a, b, and c to themultiplexer 163. As indicated in FIG. 4J, the multiplexer 163 is made upof a corresponding plurality of relays which are energized to apply aselected output as derived from one of the pressure transducers to theA/D converter 166. The PI/O circuit 168 determines which of the relaysof the multiplexer 163 is to be energized by applying control signalsvia the bus 169 to the logic circuit 165 comprised of a binary codeddecimal to decimal converter and decoder 165a, which in effect selectswhich of the relays of the multiplexer 163 to be energized and applies ahigh going signal via a corresponding output via a set 165b of logictranslators to a corresponding set 165c of power drivers, whereby acorresponding relay of the multiplexer 163 is energized to apply thecorresponding temperature output to the A/D converter 166. Next, thePI/O 168 applies a convert signal via conductor 159 to the A/D converter166, which converts the inputted analog signal to a correspondingdigital signal, and transmits a status signal to the PI/O circuit 168.

In FIG. 4K, there is shown a schematic diagram of the conditioningcircuit 134 as generally shown in the functional block diagram of FIG.4C. The PI/O circuit 184 is shown as being coupled by the I/D bus 140 tothe CPU 120 and being coupled to the counter 182 comprised of a pair ofcounters 182a, 182b. In turn, the signal conditioner and logic circuit170b is shown as comprised of a series of NOR gates 172 whose output isapplied via a NAND gate 180 and an inverter to an input of the counter182a. The output of the linear encoder 26 is applied via correspondinglogic translators and inverters to the aforementioned NOR gates 172 ofthe signal conditioner and logic circuit 170b. The rotary meter encoder40 is applied to the signal conditioner and logic circuit 170a that issimilar to the signal conditioner and logic circuit 170b to provide acomposite signal to the interval timer 174 and a conditioned signalcorresponding to the A signal to the interval timer 176. It isunderstood that the I/D circuits designated 174 and 176 of FIG. 4K, alsoinclude the programmable counters 174a and 176a, respectively. Theoutput of the interval timer 174 is applied via the logic circuit 177comprised of a NAND gate and a pair of NOR gates as shown in FIG. 4K, tothe Interrupt 2 input of CPU 120. The output of interval timer 176 isapplied to the control board of the servomotor 20.

As shown in FIG. 4K, the signal conditioner and logic circuit 170a iscomprised of first and second inputs receiving respectively the outputsignals A and A as developed by the rotary meter encoder 40. As shownrespectively in FIGS. 11A and 11B, the A signal lags the A signal toprovide, as will be explained, an indication of the direction ofrotation in which the meter encoder 40 is moving. It is understood thatthe meter encoder 40 is designed for this particular system to rotate ina clockwise direction, and if jitter or mechanical vibration is imposedupon the meter encoder 40, at least momentarily, the A signal may appearto be leading the A signal; FIG. 11C shows the output signal A as itwould appear as if it leads the A signal by 90°, this condition beingundesired, indicating an erroneous signal condition. The signalconditioner and logic circuit 170a is designed to eliminate suchconditions as will now be explained. The A and A signal are each appliedthrough a level shifter and inverter circuits to NOR gates 181a and181b, respectively. The output of the NOR gate 181a is coupled to aninput of the NOR gate 181b and the output of the NOR gate 181b iscoupled via an inverter to an input of a NOR gate 181c. As shown in FIG.4K, an inverted signal, i.e., 180° out of phase with an input to the NORgate 181a, is supplied to a NOR gate 181d, whose output is applied tothe other input of the NOR gate 181c. The effective output of the signalconditioner and logic circuit 170a is derived from the output of the NORgate 181c as shown in FIG. 11D, assuming that the meter encoder 40 isrotated in a clockwise or desired direction, and is applied to theinterval timer 174 to be counted as explained above. However, if even ona relatively short time basis, the A signal appears to be leading the Asignal, a DC (or logic zero signal) output signal will be derived fromthe NOR gate 181c indicating the presence of jitter or some othererroneous signal. In similar fashion, the signal conditioner and logiccircuit 170b receives the A and A signal as derived from the linearencoder 26, these signals being also illustrated by FIGS. 11A and 11Brespectively. In similar fashion, the A and A signals are applied to asimilar set of NOR gates 169a, b, c, and d. The output of NOR gates 169cis applied to a latch as comprised of a pair of NOR gates interconnectedas shown in FIG. 4K. In similar fashion, if the A signal as derived fromthe linear encoder 26 is lagging its A signal, the output as shown inFIG. 11C will be applied via the latch 169e to the interval timer 176 tobe counted by its counter 176a. A further set of NOR gates is alsoincluded in the signal conditioner and logic circuit 170b to provide anoutput signal as applied to the input 22 of the interval timer 176 toindicate the occurrence of the A signal leading the A signal as derivedfrom the linear encoder 26, indicating that the piston 14 is beingdriven in a reverse condition, i.e., is being driven by the servomotor20 in a downward direction toward its park position.

In FIG. 4L, there is shown a schematic diagram of the signal conditionerand logic circuit 136 as generally shown in FIG. 4D. Data is transferredbetween the parallel data controller (PDC) 192b and the CPU 120 via theI/D bus 140 and direct connections to the CPU 120. The output of the PDCcircuit 192b is coupled to a logic circuit 190b and by a plurality oflines as shown on the right-hand side of the PDC 192b. The logic circuit190b is primarily comprised of a logic translator connected to each ofits output. A NAND gate is incorporated into the logic circuit 190b toprovide a reset signal to the printer 111a. As shown in FIG. 4L, astrobe signal is applied to the printer 111a which in turn applies anacknowledge signal (ACKO) to the PDC circuit 192b, whereby data may betransmitted to be printed by the printer 111a under the control of a setof signals so marked. In addition, a busy signal may be developed by theprinter 111a to inhibit the transmission of data from the PDC circuit192b to the printer 111a. Further, the SDC circuit 192a is coupled viathe I/D bus 140 and direct connections to the CPU 120; its output astaken from the right-hand side of the SDC circuit 192a is applied viathe logic circuit 190a to provide data into and from the CRT terminal112 under the control of preselected signals as provided by thecircuitry as shown on the left-hand side and designated control;briefly, the control signals provide fixed signals to determine the modeof operation of the CRT terminal 112. The logic circuit 190a coupled tothe data out signal comprises a logic translator and an inverter circuitin the form of a line driver while the data input line is processed toinvert the signal before application to the SDC circuit 192a. The clockcircuit 193 applies a signal via a logic circuit 195 comprised of logictranslators to the clock inputs of the SDC circuit 192a.

The signal conditioning circuit 138 as generally shown in FIG. 4E ismore completely shown in the schematic drawing of FIG. 4M. The PI/Ocircuit 200 is coupled to the CPU 120 by the I/D data bus 140 and thosedirect connections at the top and bottom so indicated. The outputs asvariously taken from the PI/O circuit 200 are coupled by the logiccircuit 198a to variously energize the lights as shown on the systemcontrol and display unit 111. The logic circuit 198a is comprised of alogic translator for each output of the PI/O circuit 200 and a pluralityof drivers to energize the corresponding lights. In addition, signalsfrom the switch mechanisms of reset and stop pushlites 111f and 111g areapplied via the logic circuit 198a and in particular to a set of NANDgates as shown in FIG. 4M whose outputs are applied via inverters to thePI/O circuit 200. A second PI/O circuit 196 is coupled by the I/D databus 140 and direct connections to the CPU 120. A set of its outputs areapplied via a logic circuit 194a to control various functions includingdirection and velocity of the servomotor 20; the logic circuit 194areceives seven inputs that are coupled via a set of NOR gates and seriesconnected inverters and logic translators to a corresponding pluralityof drivers, whose outputs serve to control the direction and velocity ofthe servomotor 20. Further, two outputs of the PI/O circuit 196 areapplied via a logic circuit 194b comprised of a series connectedinverter and a logic translator to a driver before being applied tocontrol the pneumatic solenoids 66 and 64 associated with the valves 34and 36. A set of five inputs are derived from the logic circuit 194cwhich processes inputs from the proximity detectors 50, 52, and 54; thelogic circuit 194c comprises a circuit of resistors and diodes ascoupled via inverters to corresponding inputs of the PI/O circuit 196.The logic circuit 194d is coupled to the logic circuit 170a shown inFIG. 4C and comprises a series of NOR gates, the input signal comprisinga one-second clock signal to control the sampling of the variouspressure and temperature signals.

Referring now to FIG. 5, there is shown a high level flow diagram of thevarious steps of the program as stored within the PROM 124 and executedunder the control of the CPU 120 using data as entered into the RAM 126.Initially, the power is applied to the computer system in step 210.Typically, the power supply for the computer system as shown in FIG. 3can take the form of that supply as manufactured by Power Mate undertheir designations Power Mate EMA 18/24B and EMA 12/5D; AnalogDevices-925; Datel-MPS 5/12, MPS 5/3, and MPD 12/3; and PracticalAutomation-PS6-28. Thereafter, step 214 zeroes or erases the storagelocations within RAM 126, before entering an initializing subroutine300, whereby the various portions of the computer system are initializedas will be explained later in detail with respect to FIGS. 6A and 6B. Itis noted that at various points during the course of the program, areturn is made via entrance point 212 to step 214 to restart theoperation of the program. As shown in FIG. 4B, there is a switch 139 tobe set to indicate whether it is desired to calibrate parts of theprover system 10 or to run a meter test. If the switch 139 is disposedto its calibrate mode, the decision step 216 moves to step 400 wherein asubroutine is executed to calibrate the various analog inputs such asderived from the temperature and pressure measuring devices as shown inFIGS. 1 and 2A, and the corresponding A/D converters to which thesesignals are applied, as will be explained in more detail with respect toFIG. 7. As the system moves to step 500, the operator can recall datafrom the various input measurng devices such as temperature measuringdevices 42, 44, 48, and 57; the pressure measuring devices 51 and 46;and the output of the linear encoder 26. In addition, the operator mayalso initiate various of the meter self-tests. This subroutine will bedescribed in more detail with respect to FIGS. 8A to P. After gatheringthe appropriate data, the program moves to step or routine 900 wherein atest or a series of tests of a meter 38 is carried out by the meterprover system 10 and the results thereof displayed or recorded upon theCRT or printer. The routine 900 will be explained in more detail withrespect to FIGS. 9A to Q.

Referring now to FIGS. 6A and 6B, there is shown the initializingroutine 300 wherein in step 302, a command is sent via the I/D bus 140to cause the logic circuit 198a, as shown in FIG. 4E, to energize thestandby lite 111e. In step 304, a scaling factor corresponding to a onecubic foot test is transferred from the RAM 126 to the programmablecounter 174a within the interval timer 174 as shown in 4C, toappropriately scale the output of the meter encoder counter 179a wherebyupon counting an appropriate number of pulses, e.g., 40,000, the logiccircuit 177 outputs a pulse indicative that one cubic foot of fluid hasbeen drawn through the meter 38. Next, in step 306, the interruptsassociated with the CPU 120 are enabled to permit at any time later inthe program the interrupts to be executed if the operator, for example,depresses the reset pushbutton 111f or the stop pushbutton 111g. Up tothis point in the initialization subroutine 300, the interruptsassociated with the pushbuttons 111f and 111g could not be enabled, butafter execution of step 306, these interrupts are available to beserviced. Next in step 308, the circuitry shown in FIG. 4C as associatedwith the rotary meter encoder 40 is initialized. In particular, thelogic circuit 170a is initialized, the interval timers 174 and 176 arecleared, the PI/O circuit 184 is disposed to a selected mode, the logiccircuits 177 and 178 are reset and the programmable counters 174a and176a are programmed with the factors to be entered therein to be counteddown. In step 310, a command is sent via the PI/O circuit 196 to thelogic circuit 194b to effect opening of the second exhaust valve 36. Inparticular, the proximity detector associated with the valve 36 isaccessed and if the valve 36 is not open, the program will wait untilthe valve 36 is open. Further in step 310, the control circuitryassociated with the servomotor 20 is initialized in that the speed ofthe servomotor 20 is set to zero, and a signal is applied to theservomotor 20 to maintain it in a stationary condition, while a logiccircuit for sensing the torque of the servo-motor 20 is reset; the notedlogic circuit is coupled to sense the control current flowing to theservomotor 20. In step 312, the logic circuit 192b is initialized to itsstatic I/O mode with "hand-shaking" output capabilities, and the logiccircuit 190b clears and prepares the associated printer 111a to beginprinting. In step 314, the SDC 192a is programmed to insure that thedata may be transmitted between the CRT terminal 112 and the CPU 120,and the logic circuit 190a of FIG. 4D similarly instructs CRT terminal112 to clear and prepare itself for operation to receive data as well asto clear the CRT display. Next in step 316, any data stored in the A/Dconverter 166, as shown in FIG. 4B, is cleared and the multiplexer 163is set to its first channel whereby the output of the transducer 51 isapplied by the multiplexer 163 to the A/D converter 166. Step 318 clearsthe conditioning and interface circuit 130, and in particular clears anydata stored in the A/D circuit 158, as shown in FIG. 4A, as well as toset the multiplexers 149 and 154 to their first channels whereby theoutput voltage of the prover temperature transducer module is appliedvia the multiplexers 149 and 154, and the operational amplifier 152 tothe A/D circuit 158. In step 320, command signals are sent via the I/Dbus 140, and the PI/O circuit 196, as seen in FIG. 4E, to cause thelogic circuit 194b to actuate the solenoid 66 to open and then close thefirst or meter valve 34 and to actuate the solenoid 64 to close thesecond or exhaust valve 36. When it is desired to open or close one ofthe valves 34 or 36, the proximity detector associated therewith isinterrogated and if it is determined to be in the desired position, nofurther action is taken; if, however, the valve is not in the desiredposition, the logic circuit 194b provides an output to actuate theassociated pneumatic solenoid to cause the valve to open or close, asdesired. In steps 322, the program continues to a subroutine as will beexplained with respect to FIG. 6B whereby the piston 14 is returned toits park position, i.e., the lowermost position corresponding to theposition of the proximity detector 50 as seen in FIGS. 1, 2A and 2B.

In FIG. 6B, the subroutine 322 for returning the piston 14 to itslowermost position is shown. In step 324, a control signal is sent viathe I/D bus 140, the PI/O circuit 196 to cause the logic circuit 194b toclose the first or meter valve 32. Next, step 326 determines theposition of the piston 14 which may be anywhere from its lowermost toits topmost position as seen in FIG. 1; in particular, step 326 causesthe PI/O circuit 196 to interrogate the logic circuit 194c to determineif the output of the proximity detector 50 as seen in FIGS. 1 and 2 ishigh or one, and if so, the subroutine moves to the final step 346wherein a command is sent to the PI/O circuit 196 of FIG. 4E tocondition the logic circuits 194a and 198b so that the motor control forthe servomotor 20 is set for zero speed and further to set the intervaltimer 176 as seen in FIG. 4C to indicate that the output of the encoderis in its starting position, i.e., to set the counter 176a to zeropreparing it to start generating one second sampling pulses. If thepiston 14 is not at its park position, the subroutine proceeds to step328, wherein a determination is made as to whether the piston 14 isdisposed in an intermediate position, i.e., the abutment 92 is disposedbetween the proximity detectors 50 and 52 as shown in FIGS. 1 and 2A andB; if piston 14 is so disposed, the subroutine moves to step 330,whereby control signals are sent via the PI/O circuit 196 to set thelogic circuit 194a to drive the servomotor 20 in a counterclockwisedirection, and further in step 332, the speed is controlled toaccelerate to a selected speed, i.e., the ninth of sixteen speeds.However, if step 328 determines that the piston 14 is in its uppermostposition, i.e., its abutment 92 is above the proximity detector 52, step334 sets the logic circuit 194a of FIG. 4E to set the lowest speed,i.e., speed 1 of 16 and to rotate the servomotor 20 in acounterclockwise direction, before proceeding to step 336 wherein thelogic circuit 194a effects acceleration of the servomotor 20 to its nexthighest speed up to a maximum of its twelfth speed. At that point instep 338, the logic circuit 194c is accessed to determine whether thepiston 14 is disposed at the proximity detector 52 and if not, step 336accelerates the piston to its next higher speed until step 338determines that the piston 14 is at the proximity detector 52. At thatpoint, the logic circuit 194a maintains the current speed of servomotor20, until in step 342, the park proximity detector 50 detects thepresence of the piston 14 at which time, step 344 controls the logiccircuit 194a to decelerate the piston 14 to a stop position beforeentering the step 346 wherein the motor control is set for zero speed.

If the operator has set the calibrate/run switch to its calibrateposition, the program moves to the subroutine 400 as more fully shown inFIG. 7. Initially in step 402, a command is sent to the logic circuit190a of FIG. 4D to clear the CRT terminal 112. Step 404 displays asuitable message upon the CRT screen indicating the meter prover system10 has entered into a calibrate mode indicating, as shown in FIG. 7, thevarious parameters that may be so calibrated. Next, step 406 returns thecursor as displayed upon the CRT to its left-hand margin waiting for theoperator to make a suitable entry. Next after operator entry via thekeyboard of the CRT terminal 112, step 408 interrogates the keyboard todetermine which of the possible keys has been depressed. For example, ifit is determined that one of the sets of keys T and O, T and 1, T and 2,T and 3, T and 4, T and 5, T and 6, or T and 7 has been depressed, thesubroutine moves to step 410, wherein a corresponding channel isselected by the multiplexer 149. Next in step 412, a select commandsignal is transmitted via the PI/O circuit 160 to the multiplexer 149,whereby the selected channel is connected via the multiplexers 149 and154, the amplifier 152, to the A/D converter 158. Next, step 414 appliesa convert signal to the A/D circuit 158 whereby in step 416 thetemperature as measured is displayed. At this point, the operator cancalibrate the selected temperature transducer module to provide acorrect reading by adjusting the zero and span of the operationalamplifier of the module, this procedure being repeated until an accuratereading is displayed upon the CRT. Though detailed explanation will notbe given, it is realized that the similar keys P and 1, P and 2, and Pand B may be also operator activated, whereby the gains of theoperational amplifiers 161a, 161b, 161c of FIG. 4B may be similarlyadjusted in order to give accurate readings. In similar fashion, thekeys T and O, T and 1, T and 2, T and 3, T and 4, T and 5, T and 6, Tand 7, may be depressed and their respective amplifiers and circuits maybe adjusted to provide accurate readings. Upon pressing of the keys Vand P, as determined by step 408, the routine moves via step 450 to step452, whereby a command signal is sent via the PI/O circuit 168 of FIG.4B to cause the multiplexer 163 to apply the voltage calibrate inputsignal V to the A/D converter circuit 166, which converts these inputsin step 454 to digital values. The voltage calibrate input signal isadjusted to set the zero and full scale values of the A/D converter 166,these values being appropriately displayed in step 456 upon the CRTterminal 112. In similar fashion if the V and T keys of the keyboard isdepressed, the routine proceeds via step 442 to step 444, wherein thevoltage calibrate input signal VT is applied to the A/D convertercircuit 158 of FIG. 4A and its zero and full scale values may besimilarly adjusted. If any other key is depressed upon the keyboard,step 408 branches via step 456 to step 458, wherein that character isrejected to return to the starting point of step 408 again.

The data input and retrieval subroutine as broadly shown in FIG. 5 asstep or routine 500, is more fully explained with respect to FIGS. 8A to8P, an overview of the routine 500 being shown in FIG. 8A. Initially, acommand is given via the I/D bus 140 to the logic and driver circuit198a of FIG. 4E to energize the standby light 111e. Next in step 504,which is more fully shown in FIG. 8C, a determination is made if aself-test is desired, and if so, that subroutine is executed. Next instep 506, it is determined whether it is desired to display the roomtermperatures, and if so, a display upon the CRT of the terminal 112 ismade, as will be more fully explained with regard to FIG. 8H. In step508, an examination of the keyboard is made to see if the operatorwishes to recall data pertaining to previous meter accuracy tests and ifany data is required, that data is displayed upon the CRT display; thesubroutine 508 will be more fully explained with regard to FIG. 8J. Instep 510, appropriate flags are set automatically to permit, at a latertime during the meter test, the pressure and temperature parameters tobe monitored and displayed; the subroutine for executing such display ismore fully explained with respect to FIG. 8K. In step 512, thesubroutine for setting the test volume desired and the manner in whichit is entered into the programmable counter 174a of the interval timer174 is set out in more detail with the subroutine as shown in FIG. 8L.Next, it is necessary for the operator to enter via the CRT terminalkeyboard a select test flow rate or rates, as will be more fullyexplained with regard to the subroutine of FIG. 8M. In step 516, theoperator sets the number of times to repeat a certain test; for example,the meter may be tested three times for a flow rate or for a selectedvolume and flow rate. The entry of the repeat commands is explained withrespect to the subroutine of FIG. 8N. Thereafter, step 518 sends clearcommands via the logic circuit 190a whereby any data stored in thebuffers associated with the CRT terminal 112 are cleared. At this point,step 520 makes a decision as to whether the volume of the meter 38 is tobe determined with the output of the proximity detector 27 or with theoutput of the rotary encoder 40. If the switch is set to a logic "zero",a flag is set in step 522 to conduct an encoder type test, whereas ifthe switch is set to a logic "one" position, a flag is set in step 524to conduct the proximity detector type test.

Continuing the routine 500 as shown in FIG. 8B, the system obtains anddisplays upon the CRT the meter temperature and pressure, and the provertemperature and pressure as measured during the meter test, as follows.Next, step 528 displays, if instructed, upon the CRT data indicative ofthe pressure and temperature within the meter 38 and the prover 10. Oncethe test volume, either one cubic foot, one-half cubic foot, orone-fourth cubic foot, has been set by entry of the operator upon theCRT terminal 112, the entered value is decoded in step 530, the chosenvalue is displayed in step 532 by the CRT as: TEST VOL.=x CU. FT.Thereafter, the desired flow rate or rates that are entered upon thekeyboard are decoded in step 534 and the chosen rates are displayed uponthe CRT in step 536 as: FLOW RATES are QX, QX - - QX. In similar fashionin step 538, the number of repeats for any particular test(s) withrespect to flow rates or volumes are decoded and in step 539, theselected number of repeats per flow rate or volume is displayed upon theCRT as: NO. OF TESTS PER FLOW RATE=X. At this point, a carriage returnline feed instruction is carried out in step 540 whereby a cursor asplaced by the CRT terminal upon the CRT is removed.

The subroutine 504 is more fully shown in FIG. 8C, wherein a desiredself-test(s) is selected. Initially in step 542, the data storagebuffers associated with the CRT of the CRT terminal 112 are cleared bycommands generated by the logic circuit 190a. In step 544, the CRTdisplays, as shown in FIG. 8C, an indication of the various self-teststhat may be conducted, e.g., volume V, leakage L, or NO; the operatorselects one of these self-tests by depressing the appropriate key of thekeyboard. In step 546, the cursors, as shown in FIG. 8C, are flashed toprompt the operator to respond to select the self-tests, whether volumeV, leak L or NO. In step 548, the subroutine moves to the desiredself-test dependent upon which key has been selected in step 544. If forexample, the volume self-test V has been selected, a volume self-testsequence is output to the CRT in step 552 and the volume self-test isexecuted in step 554 as will be more fully explained with respect toFIG. 8E. If a leak test has been chosen, the subroutine moves throughstep 558 to provide a display upon the CRT indicating the selected testand to initiate the leak self-test, which is executed in step 560 aswill more fully be described with respect to the subroutine of FIG. 8D.Next the subroutine determines in step 556 whether there is anotherinput to be dealt with and the subroutine returns to step 546. If theoperator pressed the escape key as determined by step 548, thesubroutine exits via step 562 to the entry point 212 of the main diagramas shown in FIG. 5 wherein the program begins. If the operator strikesthe N and O keys, as detected by the steps 548, the subroutine exits viastep 566 and returns to the routine as shown in FIG. 8A to continue withthe next step 506. If any other key is struck, the subroutine exits viastep 568 to reject that character in step 570 and to return to step 548to recognize another key.

The leak self-testing subroutine 560 is more completely shown withrespect to FIG. 8D. The leak self-test is a test to provide anindication of the integrity of the prover system's seal. Initially instep 572, the logic circuit 198a in FIG. 4E energizes the self-test andtest in progress lights 111b and 111c. Next, the subroutine 322 forreturning the piston to its park position as explained above withrespect to FIG. 6B, is executed. Next, a command signal is issued instep 574 via the PI/O circuit 168 to set the multiplexer 163 to receivethe signal via the second channel from the pressure transducer 51(pressure PP1). Next, the logic circuit 194b is commanded to applyactuating signals to the solenoids for effecting the closing of thefirst inlet and second exhaust valves 34 and 36. In step 578, a commandis issued via the PI/O circuit 196 to actuate the logic circuit 194a ofFIG. 4E to direct the servomotor 20 to drive the lead screw 18 in aclockwise direction at a relatively slow speed corresponding to "1". Theservomotor 20 cannot be energized as directed by step 578, until theprohibition built into the program is defeated as by depressing amomentary switch (not shown) coupled to the logic circuit 194c, therebypermitting the operation of the servomotor 20 with both valves 34 and 36closed. Normally, the servomotor 20 may not be operated if the valves 34and 36 are closed, thus preventing possible damage to the piston seal.Next, an indication of pressure is input into the A/D converter 166 instep 580 and a check is made in step 582 to determine whether thepressure has increased by a certain amount as indicated by the datastored in the A/D circuit 166, i.e., has the vacuum increase exceeded1.38 inches of water? If the vacuum has not increased to beyond 1.38inches of water, the subroutine cycles back and repeats step 580. If thevacuum inside the chamber 28 has increased to beyond 1.38 inches ofwater, the subroutine moves to step 584 whereby a command is giventhrough the PI/O circuit 196 to cause the servomotor 20 to stop. In step586, a 20-second wait is loaded into a register within the RAM 126 andcounted down to provide a time for leakage to occur in the chamber 28.Next, in step 588, a convert signal is applied to the A/D converter 166of FIG. 4B, to determine the pressure now being sensed by the pressuretransducer 51. In step 590, the subroutine waits for the one-secondclock signal which is developed from the logic circuit 178 of FIG. 4Cand is applied via the logic circuit 194d of FIG. 4E to decrement instep 592 the 20-second count placed in the register within the RAM 126.Step 592 determines whether this register in the RAM 126 has beendecremented to zero, and if not, the subroutine returns to step 588,whereby for each second of a 20-second interval, the piston pressure asderived from the transducer 51 is obtained and is displayed upon the CRTthus providing a continuous monitor of the prover pressure so that theoperator may determine whether there are any leaks within the chamber 28during the 20-second test. The count decrementing continues until theregister is zero as determined by step 592, at which time a command isissued in step 594 to cause the logic circuit 194b to actuate thesolenoid to open the second exhaust valve 36. At this point, theposition of the piston 14 is determined in step 596 by checking thestatus of the proximity detectors 50 and 52 by accessing the logiccircuit 194c. At this time the test is complete and a command is issuedto the logic circuit 190a to energize the test complete and self-testindicators. Finally, in step 322, the piston 14 is returned to its parkposition by the subroutine as shown in FIG. 6B, before returning to step556 as shown in FIG. 8C.

In FIG. 8E, the volume self-test subroutine 554 is shown in more detail.First, step 600 commands the logic circuit 198a to energize theself-test and test in progress indicators 111b and 111c. The volumeself-test is entered to obtain an indication of the accuracy of thelinear encoder 40. Step 332, as shown in FIG. 6B, returns the piston 14to its park position before command signals are issued in step 602 viathe logic circuit 194b to actuate the solenoids to open the first, inletvalve 34 and to actuate the solenoid to close the second exhaust valve36. Next, a command is made in step 604 to load the speed buffer, i.e.,an addressed portion within the RAM 126, with its maximum speed of 16.Next in step 606, the servomotor 20 is accelerated to the speed asstored in this buffer in accordance with the subroutine as will bediscussed with respect to FIG. 8F. Next in step 608, the counter 182 andthe programmable counter 174a as shown in FIG. 4C are inhibited and arereset to zero. Step 610 checks the status of the proximity detector 52to determine whether the piston 14 has been drawn to its start-testposition, and if not, the check is repeated until the piston 14 reachesthis position. When the piston 14 has reached its start-test position,the program moves to step 612 wherein the programmable counter 174a isdisabled and the linear counter 182 is enabled to count the linearencoder pulses as the piston 14 is drawn from the proximity detector 52to proximity detector 54. In step 614, the status of the disabledproximity detector 54 is checked periodically until the piston 14 isdisposed thereat, at which time the subroutine moves to step 616 todisable the linear counter 182. In step 618, the cumulative number orcount from linear encoder counter 182 is transmitted via the PI/Ocircuit 184 to a designated location within the RAM 126. In step 620, asuitable series of command signals are transmitted to the logic circuit194a whereby the servomotor 20 is decelerated to a stop condition aswill be described with respect to the subroutine shown in FIG. 8G. Nextin step 622, flags are set indicating that the piston 14 is not betweenthe proximity detectors 50 and 52. In step 624, the logic and drivercircuit 198a energizes the self-test and test complete lights 111b and111d. At this point in step 626, the count of the counter 182 indicativeof the travel of the piston 14 between the proximity detectors 52 and 54is transferred from its location within RAM 126 to be displayed by theCRT of the terminal 112 and at the same time clears counter 182. Next,the piston 14 is returned to its park position by step 332 as shown inFIG. 6B, and step 628 causes the logic and driver circuit 198a toenergize the standby light 111e, before returning to step 556 as shownin FIG. 8C.

The accelerating motor subroutine generally indicated in FIG. 8E by thenumeral 606 is shown in more detail in FIG. 8F, wherein in step 630 acommand is sent via the I/D bus 140 to disable the counters 182 and 174aof FIG. 4C. Next, an enable command is sent to the logic circuit 194a bystep 632 to command the servomotor 20 to rotate in a clockwisedirection, thus raising the piston 14. At this point, speed 1, i.e., thelowest speed, is loaded into a speed compare buffer within the RAM 126by step 634. In step 636, a command is given to the logic circuit 194ato increase incrementally the speed of the servomotor 20 and the actualspeed as stored in the speed compare buffer of the RAM 126 is comparedwith the final designated speed stored in the speed buffer and if theyare equal, i.e., the servomotor 20 has been accelerated to the desiredspeed, the subroutine moves to step 646. If not, step 640 implements await period of approximately 0.25 seconds before sampling via the logiccircuit 194c the status of the proximity detector 52 and if not at thisposition, step 644 increments the desired speed by 1 before returning tostep 636 in which the new speed is disposed in the speed compare bufferof the RAM 126. If the piston 14 has been driven into its intermediateposition as detected by step 640, the subroutine moves to step 642, toset a flag indicating that the piston 14 has been prematurely brought toits intermediate position and the subroutine is returned to step 604, asshown in FIG. 8E. As seen in FIG. 8F, the normal operation is for thepiston 14 to be accelerated to the desired speed and then toperiodically test the output of the proximity detector 52. Upondetermining in step 646 that the piston 14 has reached the start-testposition as indicated by the output of the proximity detector 52, thesubroutine branches to step 970 as will be explained with respect toFIG. 9E to assess and determine the occurrence of the rising edge of thenext pulse A from the rotary meter encoder 40, whereby as will beexplained further the meter test is begun by applying the pulse outputsderived from the rotary meter encoder 40 and the linear encoder 26 intotheir respective counters 174a and 182.

The subroutine to decelerate the servomotor 20 as indicated in step 620of FIG. 8E is more fully explained with respect to the subroutine shownin FIG. 8G. Initially in step 648, the counter 174a and the counter 182as seen in FIG. 4C for respectively receiving the rotary and linearencoder outputs are first disabled and then reset. In step 650, the loadspeed compare buffer within the RAM 126 is loaded with the speed, 16,i.e., the highest speed available. Next, in step 652, the actual speedas stored in the speed buffer of RAM 126, is compared with the highspeed 16 as loaded into the speed compare buffer and if not equal, thespeed as loaded into the speed compare buffer is decremented until theactual speed equals the speed loaded into the speed compare buffer, atwhich time the subroutine moves to step 656 and the speed as stored inthe speed compare buffer is decremented. In step 658, a command isissued to the logic circuit 194a to decelerate the servomotor 20 to thatnew speed as disposed within the speed buffer of the RAM 126. In step660, the actual speed is compared with zero, i.e., the servomotor 20 isstopped, and if not stopped, a 0.2 second wait or delay is implementedin step 662, before again decrementing the motor speed by steps 656 and658. This process continues until the servomotor 20 has been brought toa stop, i.e., the speed equals zero at which time step 660 returns thesubroutine to step 622 of FIG. 8E.

In FIG. 8H, there is shown the subroutine 506 for operator entry via thekeyboard of the CRT terminal 112 of the selected temperatures within theprover room 106 to be displayed and the steps for so displaying themupon the terminal's CRT. It has been shown that knowledge of thetemperature within the prover room 106 is helpful to investigate thelevel of control that may be exercised upon the meter prover 10 withinthe room 106. The subroutine as shown in FIG. 8H permits the operator todisplay any of the four room temperature outputs R0, R1, R2, and R3,from the temperature measuring devices shown within FIG. 2C as beingdisposed about the prover room 106. These temperatures can continue tobe accessed and displayed upon the CRT of the terminal 112 until theoperator terminates this action by pressing the N and O keys of theterminal's keyboard. Initially in step 664, a command is sent to thelogic circuit 190a, whereby via the control input, the buffersassociated with the CRT terminal 112 are cleared. Thereafter, step 666causes the logic circuit 190a to display an indication, as shown in FIG.8H, of the possible room temperature devices that may be accessed, i.e.,the room temperature devices R0, R1, R2, or R3. If the operator does notdesire to access and display any of these temperatures, the N and O keysare struck. In step 668, a carriage return line feed is output so thatthe cursor is flashed, indicating that an operator response is required.In step 670, an interrogation is made of which key is actuated via thelogic circuit 190a and if the keys R and O corresponding to the roomtemperature device R0, are actuated, the subroutine moves via step 672ato step 674a whereby a control signal is issued via the I/D bus 140,PI/O circuit 160 to cause the multiplexer 149 to select its fifth inputwhereby a voltage representative of the room temperature transducer R0is applied via the multiplexers 149 and 154 to the A/D converter 158. Instep 676a, a convert signal is applied via the PI/O circuit 160 to theA/D converter circuit 158 to convert the analog input signal to binarydigital data. Next, step 678a converts the binary digital data todecimal data and, step 680a converts that data to a floating pointdecimal format by processes well known in the art. In step 682 a, thedigital floating point decimal data is converted to digital F° inaccordance with the formula: ##EQU1## In step 684a, suitable data isgenerated out from the logic circuit 190a to display the roomtemperature in degrees Fahrenheit upon the CRT display. In similarfashion, step 670 is able to detect the operator actuation of each ofthe pairs of keys corresponding to R0, R1, R2, and R3 room detectors toaccess these detectors as connected to the multiplexer 149 of FIG. 4Aand to process and display the selected data upon the CRT display. Instep 694, a determination is made as to whether another input isdesired, and the process returns to the beginning of step 670. If theoperator presses the escape key, the routine moves through step 686 toreturn via entry point 212 to the beginning of the program as seen inFIG. 5. If the N and O keys are depressed, the program proceeds to step688 and returns to the next subroutine or step 508 as seen in FIG. 8A.If an extraneous key is depressed, the subroutine exits through step 690and rejects the character in step 692 before returning to the beginningof step 670.

The subroutine 508 as generally indicated in FIG. 8A for sampling datafrom previously conducted tests is carried out by the subroutine 508which is more clearly shown in FIG. 8J. The subroutine may be enteredafter a meter test has been executed. First, in step 696, the CRT, inparticular its buffers and display, are cleared of previously storeddata. Next, step 698 displays by actuating the logic circuit 190a tohave the CRT display the possible test parameters that may be accessedand displayed, namely K, the number of counts from the linear encoder26; TP, the temperature of the prover; TM, the temperature of the meter;PM, the pressure of the meter; PP, the pressure of the prover; and thepercentage of error from the previous test. If none of these values aredesired to be displayed, the operator may depress keys N and Ocorresponding to NO at which time the program advances to the next step.In step 700, the cursor is flashed indicating to the operator to selectone of these parameters or NO by pressing the corresponding key. In step702, if the linear encoder counts are selected by depressing the key K,the subroutine branches through step 704a to step 706a, whereby thecount of the linear encoder register within the RAM 126 is accessed andread out and applied via the logic circuit 190a to be displayed upon theCRT. In similar fashion, if the keys corresponding to the temperature ofthe meter prover are actuated upon the keyboard by the operator, theprocess proceeds from step 702 via step 704b to step 706b wherein thecontents of the prover temperature buffer, a designated location withinthe RAM 126, is transferred from the RAM 126 to be displayed upon theCRT. In similar fashion, each of the meter temperature TM, the provertemperature TP, the prover pressure PP, or the meter pressure PM may besimilarly accessed from a corresponding location within the RAM 126 anddisplayed upon the CRT. Also the percentage of error of the differencebetween the standard volume as drawn by the prover system 10 and thatactually measured by the meter 38 is calculated with respect to thestandard volume and may be likewise displayed upon the CRT. If a secondor further key has been pressed, step 716 returns the subroutine to thebeginning of step 700. If the escape key has been depressed, thesubroutine moves through step 708 to exit via entry point 212 to thebeginning of the program as shown in FIG. 5. If any extraneous key isdepressed, the routine proceeds through step 712 to reject the mistakencharacter in step 714 before returning to the beginning of step 702.After the operator has observed any and all parameters that he desiresto observe upon the CRT, he presses the N and O keys whereby the programreturns to the next step or subroutine.

Routine 510 as generally shown in FIG. 8A is capable of accessing anddisplaying the parameters as are automatically measured and monitoredduring the course of a test, and is shown in greater detail in FIG. 8K.First in step 718, the buffers associated with the CRT are cleared,before steps 720, 722, 724, and 726 set flags in appropriate locationswithin the RAM 126 to access the prover and meter temperatures and themeter and prover pressures. Thus, the flags are set to permit displayupon the CRT of these parameters automatically, and thereafter theroutine 510 returns to step 512 as shown in FIG. 8A.

Step 512, as generally shown in FIG. 8A, for setting the desired volumeto be drawn through the meter 38 is more fully explained with respect tothe subroutine shown in FIG. 8L. Initially, the CRT terminal 112 iscleared in step 742, before in step 746 displaying upon the CRT thepossible volumes, e.g., one cubic foot, 0.5 and 0.25 cubic feet, thatmay be selected by the operator to be drawn through the meter 38 to betested. In step 748, the cursor is flashed to prompt the operator tomake his volume selection. Upon actuation by the operator of the keycorresponding to each of the selectable volumes, the subroutine 512moves to enter the corresponding volume. For example, if the appropriatekey is depressed indicating a desire to enter a value corresponding toone cubic foot, the subroutine moves via step 752a to step 754a whereinthe scaling factor corresponding to one cubic foot is set in a knownposition in the RAM 126. The scaling factor will be subsequentlytransferred from this RAM location to the rotary encoder counter 174a.After selection of any of the desired test volumes, the subroutinereturns to the next step 514 as shown in FIG. 8A. If the escape key isselected, the subroutine moves through step 756 to return to the mainprogram via entry point 212. If a wrong key is accidentally depressed,the subroutine moves through step 758 to reject that entered characterin step 760 before returning to the beginning of step 750.

Next in the program is step or subroutine 514 wherein the desired flowrate at which the fluid is to be drawn through the meter 38 is set; asexplained above, the selected flow rate in turn determines the speed atwhich the servomotor 20 is controlled to rotate and raise the piston 14as shown in FIG. 1. Referring now to FIG. 8M, step 762 initially clearsthe buffers associated with the CRT terminal 112 and in step 764, thepossible flow rates from Q0 to QF are displayed upon the CRT, it beingunderstood that Q0 corresponds to a minimum flow rate, e.g., 20 cubicfeet per minute, and QF corresponds to a maximum flow rate, e.g., 400cubic feet per minute. Step 766 causes the cursor to flash on and off toprompt the operator to make his selection of flow rate. In step 768, aninterrogation is made of the keyboard to determine which key theoperator has depressed and if for example, the flow rate Q0 isdepressed, the subroutine exits via step 770a to step 772a wherein theflag for the particular rate Q0 is set in a designated location withinthe RAM 126. Next, step 774a causes the selected flow rate Q0 to bedisplayed upon the CRT; then, the system returns with the response of"ANOTHER?" and flashes the cursor to indicate that a user response isrequired. If a further rate is to be also tested, step 784 returns theroutine to the beginning of step 766 whereby a second and perhapsfurther flow rates may be tested within a single set of tests. If theoperator depresses the escape key, the routine moves through step 776and entry point 212 to the main program as shown in FIG. 5. If a wrongkey of the keyboard of the CRT terminal 112 is depressed, the routinemoves through step 780 to reject the incorrect character in step 782before returning to the beginning of step 768. If no further flow ratesare to be selected to test the meter 38, the operator presses the N andO keys, whereby the routine returns via step 778 to the next step 516 asshown in FIG. 8A.

Step or routine 516 for setting the number of repeat tests that is to beset for each of the selected flow rates may be entered via the operatorkeyboard in a manner more specifically shown in FIG. 8N. Initially, thebuffers associated with the CRT terminal 112 and the display screen ofthe CRT are cleared in step 786, before the possible number of tests orretests for flow rate, i.e., 1, 2, or 3, is displayed upon the CRT. Step790 flashes the cursor on the CRT to prompt the operator to make hisselection of the flow rate. Step 792 detects which of the terminal keysis depressed and if for example, a key is depressed indicating only onetest per flow rate is to be conducted, the subroutine proceeds throughstep 794a to step 793a, wherein the output "1" is displayed upon the CRTbefore returning to the next step 518 of the main program as seen inFIG. 8A. If two tests are to be made, the subroutine exits via step 794bto step 793b wherein a command is made to copy the flow rate flags forone repeat and in step 796b to set a flag for a second repeat in adesignated area of the RAM 126. In step 796b, an indication of 2 isdisplayed upon the CRT. If a selected test is to be repeated threetimes, the subroutine carries out a similar series of steps 794c, 793c,and 796c. If an incorrect character is depressed upon the keyboard, theroutine moves through step 795 to reject the incorrect character in step797 before returning to the beginning of step 792. If the operatorpresses the escape key, the routine exits via step 798 to entry point212 whereby a return is made to the main program as shown in FIG. 5.

Subroutine 528, as generally shown in FIG. 8A, displays temperature andpressure data as the meter test is being conducted, as more fully shownby the subroutine illustrated in FIG. 8P. Initially, the CRT cursor ismoved to a home position and the CPU 120 addresses that location withinthe RAM 126 where the TM flag has been set automatically during theprevious subroutine 510. Since the TM flag has been set, the content ofthe meter temperature buffer, i.e., an addressable location within theRAM 126, is transferred via the logic circuit 190a to be displayed uponthe CRT as indicated in step 802. After the display, the subroutinemoves to step 806 which examines that location of the RAM 126 where theTP out flag indicating that there was an indication to monitor during atest the prover temperature TP has been set, and the output of theprover temperature buffer is transferred to be displayed upon the CRT.After such display, the subroutine moves to step 810, which accesses thepreviously set meter pressue PM flag and outputs the content of thepressure buffer, i.e., a known location in the RAM 126 to be displayedupon the CRT. After display, step 814 accesses the previously set PP outbuffer flag, and the contents of the prover pressure buffer istransferred to be displayed upon the CRT. After the display of suchinformation, the subroutine returns to the next step 530 as indicated inFIG. 8B. The values output at this time correspond to the valuescurrently stored in the RAM buffers. If a test has not yet been run,zeroes are initially stored in the RAM 126 and will be output anddisplayed as TM-0.0 Deg. F. This step formats the display so that when atest begins, the system will replace the zeroes with appropriatenumbers.

The execution of the tests of the meter 38 by the meter prover system 10as well as the output of the results to the printer and CRT is performedby the routine generally shown in FIG. 5 by the numeral 900, as will nowbe explained in greater detail with respect to FIGS. 9A to 9P. In FIG.9A, there is shown a high level diagram of the various steps orsubroutines that are necessary to effect the test of the meter 38starting with step 322 as shown above with respect to FIG. 6B to returnthe piston 14 to its park position, i.e., its bottom-most normalposition with respect to the cylinder 12 as shown in FIGS. 1 and 2A.Next, routine 902, as will be more fully explained with respect to FIG.9B, determines the type of test, i.e., will the volume measured by themeter 38 be determined by the proximity detector 27, or by the rotaryoptical encoder 40 as shown in FIG. 4C, and the particular volume thatis to be drawn through the meter 38; in particular step 902 loads theappropriate volume factor into the programmable counter 174a as well asto store the appropriate divisor in the buffer EORP of the RAM 126.Next, step 904 determines for the condition that one test per flow rateis to be made, the flow rate to be executed for that test; in particularthe system addresses that location where the flow rate flags are storedwithin the RAM 126 to determine the appropriate flow rate to be used inthe particular test. If the flow rate is so located, the routine movesto step or routine 906a to determine which flow rate is to be executedand to obtain that flow rate and execute that subroutine as morespecifically shown in FIGS. 9C and D. If it is decided in step 908 thattwo tests for each flow rate are to be conducted, the routine addressesthose areas in the RAM 126 for the corresponding flow rate flags andexecutes the tests at the programmed flow rate in step 906b. If threetests per flow rate are called for, it is first determined in step 912whether the flow rate for the three corresponding rates have beenentered, and if yes, step 906c calls the flow rate flags from thedesignated locations within the RAM 126 and executes the tests of themeter 38 at these flow rate(s). Thereafter, the command is sent to thelogic and driver circuit 198a to energize the standby indicator beforereturning to step 216 as shown in FIG. 5.

Determining of the test type and volume to be measured is generallyshown as subroutine 902 in FIG. 9A, and will be more fully explainedwith respect to FIG. 9B wherein initially the programmable counter 174aand the counter 182, as shown in FIG. 4C, are disabled and reset in step918. At this point, in step 919, the status of the encoder/proximitydetector switch is determined to decide whether the fluid volume passingthrough the meter 38 is to be determined by the output of the proximitydetector 27 or by the output of the rotary encoder 40. If the output ofthe rotary encoder is chosen, the subroutine moves to step 920 to testfor the presence or status of the one cubic foot flag within thedesignated location of the RAM 126, and if present, that factor which isequivalent to one cubic foot of output pulses from the output of theoptical rotary encoder 40, is stored by step 922 in the RAM EORP, i.e.,a designated location of the RAM 126, and the factor number is loadedinto the programmable counter 174a. At this point, the subroutine movesto return to the next step 904 of the program shown in FIG. 9A. If theone cubic foot flag is not present, step 924 checks the status of theone-half cubic bit or flag and if present as determined by step 924, theprogrammable counter 174a as shown in FIG. 4C is loaded by step 926 withan equivalent count and a corresponding factor is stored in the EORPbuffer location of the RAM 126, before returning to step 904 of FIG. 9A.If the one or one-half cubic foot flags are not present, step 928 looksfor the presence of the one-fourth cubic foot flag as previously enteredby the operator into its system RAM 126, and step 930 loads theprogrammable counter 174a with a count corresponding to one-fourth cubicfoot, and a corresponding factor is stored in the EORP buffer locationof the RAM 126. If no flag is present corresponding to one cubic foot,one-half cubic foot, or one-fourth cubic foot, step 932 automaticallydetermines that a one cubic foot test should be run to test the meter38.

If on the other hand, step 919 determines that the output of proximitydetector 27 is to be used to measure the fluid flow through the meter38, the subroutine moves to step 934 wherein the status of the one cubicfoot flag within the RAM 126 is checked and if set, the programmablecounter 174a of FIG. 4C is set by step 936 with a binary numberequivalent to one cubic foot of volume and a factor, normally to 8, isset in the EORP buffer location of RAM 126 before returning to the mainprogram. If the one cubic foot flag has not been set, the subroutinemoves to step 938 wherein a check of the status of the one-half cubicfoot flag is made and if present, a factor corresponding to one-half ofone cubic foot, normally 4, is stored in step 940 in the programmablecounter 174a and also within the EORP buffer location of the RAM 126,before returning to the main program. If the one-half cubic foot flaghas not been set, the subroutine moves to step 942, wherein the statusof the one-fourth cubic foot flag is checked and if present, a factorequivalent to one-fourth of a cubic foot, normally 2, is entered by step944 into the programmable counter 174a and in the EORP buffer locationof RAM 126 before returning to the main program. If none of the one,one-half, or one-fourth cubic foot flags have been set, the subroutineautomatically in step 946 sets the meter prover system 10 to conduct atest drawing one cubic foot of fluid through the meter 38.

The next routine 904 and the following routines, as shown in FIG. 9A area series of steps to determine which of the flow rates are to beconducted and how many times each flow rate is to be tested. Referringnow to FIG. 9C, step 948 actuates the logic and driver circuit 198a toenergize its test in progress light 111c before moving to step 950 todetermine whether the fow rate(s) as stored in the RAM 126 to beconducted is one of Q0 to Q7 and if so, the routine moves to step 952awherein it is determined whether the test is to be conducted at the Q0flow rate and if yes, a speed 0 is loaded in step 954a into the speedbuffer location of RAM 126 and thereafter in step 956a, the meter proversystem 10 executes the test of the meter 38 at that selected flow rateand outputs the results to the printer, as will be more fully explainedwith respect to FIGS. 9E and F. However, if the test is to be conductedat the Q1 rate, a similar set of steps 954b and 956b are conductedwhereby the speed 1 is loaded and is executed in these respective steps.Similar sets of steps 952c to 952h, 954c to 954h, and 956c to 956h areconducted whereby corresponding flow rates are entered into the speedbuffer and are executed. If the decision in step 950 was no, the routineproceeds immediately to step 958 are shown in FIG. 9D, wherein adecision is made by examining the flags disposed in the designated areasof the RAM 126 to determine whether a flow rate of Q8 to QF has beenselected and if yes, the subroutine continues to step 960a; if not, thesubroutine returns to the next step 908 as seen in FIG. 9A. Step 960adetermines whether a meter is to be tested at the flow ratecorresponding to the flow rate Q8 and if yes, step 962a loads a speed 8into the speed buffer of the RAM 126 and at that point executes by step964a the testing of the meter 38 by the meter prover system 10 at thatspecific servomotor speed and flow rate. In similar fashion, steps 960bto 960h, 962b to 962h, and 964b to 964h are conducted whereby tests atthe various flow rates and corresponding motor speeds are conductedbefore returning to the next step which may be step 908 or 912 todetermine the number of tests per flow rate that are to be conducted.

In FIGS. 9C and 10 after the flow rate at which a particular meter is tobe tested was chosen, the actual test was conducted by steps 956 and964. The actual meter test conducted by the meter prover system 10 iscarried out in the subroutine shown in FIGS. 9E and F. First, step 966commands the logic and driver circuit 198a of FIG. 4E to energize thetest in progress light 111c. Next, step 332, as shown in FIG. 6B,returns the piston 14 to its park or lowermost position, as shown inFIGS. 1 and 2A. Step 968 commands the logic circuit 194b to effect theopening of the inlet valve 34 and closure of the exhaust valve 36. Asindicated above, a particular speed has been stored in the speed bufferof the RAM 126 and the servomotor 20 is driven under the control of thelogic circuit 194a to that speed in accordance with the subroutine 606as shown in FIG. 8F. Of significance, routine 606 senses that the piston14 has been accelerated from its park position to the start-testposition as indicated by the output of the proximity detector 52, andthat the piston velocity has stabilized. Next in step 970, the outputsas derived from the rotary encoder 40 and the linear optical encoder 26,are inhibited by the signal and logic conditioning circuits 170 a and170b, respectively, from being entered into their respective counters174a and 182, and the time divisors or factors as originally selectedbased on the test volume are entered into the programmable counter 174a.In step 972, after the piston has reached the start-test position asdetermined by step 600, the output of the rotary encoder 40 is accessedperiodically, e.g., every 40 microseconds, to detect the occurrence ofthe rising edge of the next pulse therefrom as provided at the input tothe interval timer 176. If this has not occurred, the subroutine checksin step 974 the status of the proximity switch 54 and if the piston 14is at that position, i.e., towards its uppermost position within thecylinder 12, there is an indication of a failure and the subroutineexits via exit point 975 into an interrupt subroutine as will beexplained with respect to FIG. 9G. Otherwise, upon occurrence of theleading edge of the output of the rotary encoder transducer 40, theroutine moves to step 976, wherein the A output of the rotary transducer40 is applied by the signal conditioner and logic circuit 170a to theinterval timer 174 and in particular to its programmable counter 174a.Further, step 976 enables the counter 182 to start counting the pulsesderived from the linear encoder 26, and the programmable counter 174a tocount the pulses from the rotary encoder 40. In addition, step 976enables at this point in time the counter 176a to count the system clockindicated in FIG. 4C as clock A (e.g., 200 KHz) by dividing the systemclock by an appropriate factor to output via the logic circuit 178 aone-second sampling signal, whereby the various values of temperatureand pressure are sampled. In addition, an output is derived via theinterval timer 174 to enable the logic circuit 177, which is otherwisedisabled, thus permitting an end of test interrupt to be developed andin particular to apply a one logic or high signal upon the counting downof the inputted count by the programmable counter 174a to apply a signalto the Interrupt 2 input of the CPU 120 to initiate an interruptsubroutine which will be explained in detail later with respect to FIG.9J. Next in step 528, the data in terms of the pressures andtemperatures currently being measured in the meter 38 and in the chamber28 are outputted as discussed above with respect to FIG. 8P. Next, instep 980, the status of the counter 176a within the interval timer 176is tested, and if no pulses have been accumulated, the subroutinereturns to the beginning of step 980 to wait for the ocurrence of thefirst pulse output from the counter 176a. If a pulse or pulses have beendetected at the output of the counter 176a, the subroutine moves to step982 wherein the counter 176a is reset to zero. Thus, the counter 176awill be reset to zero upon the occurrence of the one per second pulseoutput from the logic circuit 178. Next in step 984, the meter pressureMP2 as derived from the outputs of the pressure transducer 46, theprover room pressure derived from the pressure transducer PB, the proverpressure PP1 as derived from pressure transducer 51, the metertemperatures TM3 and TM 4 as derived from the temperature transducers 42and 44, respectively, and the prover temperatures TP1 and TP2 as derivedfrom the temperature transducers 57 and 48, are placed within designatedlocations within the RAM 126 to be available for the calculations to beperformed upon them, as will be explained. Next in step 986, which willbe more fully explained with respect to FIG. 9L, the pressure andtemperature data is converted to a floating point decimal form and instep 988, as more fully explained with respect to FIG. 9M, the data isaccumulated and averaged. As will be explained in detail later, thevalues of pressure and temperature within the meter 40 and within thechamber 28 are accumulated periodically, e.g., every second, from apoint in time when the volume meter test is begun until it isterminated, whereby each of the samples so taken may be summed anddivided by the number of samples to time average the temperature andpressure parameters. Thus, the temperature and pressure parameters areconsidered to be taken or monitored continuously during the test of afluid flow meter. A final sample of these parameters is taken even afterthe programmable counter 174a has counted down. Next in step 990, adetermination is made of whether the test is over by interrogating theINT2 register and if the test is over, the routine moves on to thefurther steps as shown in FIG. 9F; if not, the subroutine returns to thebeginning of step 528 to output the current values in the pressure andtemperature buffers of the RAM 126 and to continue the meter test. Thegeneration and storing of an end of test flag permits the meter test toend anywhere in the interval between the sampling pulses for taking themeasurements of pressure and temperature. Thus, as will be explainedwith respect to FIG. 9J, the end of test flag is set upon the occurrencecounting down the meter encoder register 174a within a designationportion of the RAM 126 indicating that the test has ended. However, theone-second sampling pulses derived from the logic circuit 178 of FIG. 4Cis still to occur in order to obtain the last pieces of temperature andpressure data. Thus, the subroutine as seen in FIG. 9E and in particularstep 990 permits the test to end and the final items of pressure andtemperature data to be gathered before the meter prover system 10 isshut down. The use of the logic circuit 177 to sense the timing out ofthe meter encoder counter 174a permits a rapid and efficient end of testsignal or flag to be generated. If software were employed, it would benecessary to repeatedly access the status of the programmable counter174a to determine whether it has counted down, thus consideralycomplicating the program to be stored within the PROM 124 and reducingthe accuracy of the timing of test termination.

From the above, it is seen that a meter test is initiated and terminatedin response to the output of the meter rotary encoder 40. As explainedabove, the mechanism coupling the encoder 40 to the diaphragm of themeter 38 generates, in a sense, a frequency modulated signal thus makingit desirable to initiate and to terminate the counting of its output atapproximately the same point in the cycle of rotation of the rotaryencoder 40. To this end, the piston 14 is accelerated from its parkposition to a substantially constant velocity before passing thestart-test position as determined in step 646, at which point the testassesses periodically, e.g., every 40 microseconds, the occurrence ofthe rising edge of the next A pulse from the rotary meter encoder 40.That next pulse A from the rotary meter encoder 40 initiates thecounting down of the programmable counter 174a into which has beenloaded a count indicative of the test volume to be drawn through themeter 38 under test and at the same time to initiate the counting of thecounter 182, which counts the output of the linear encoder 26 to providean accurate indication of the test volume drawn into the prover 10. Uponthe counting down of the counter 174a, a signal is applied to the logiccircuit 177 to effect a CPU Interrupt 2 which as shown in FIG. 9Jdisables the counters 174a and 182, thus terminating the counting ofeach. Thus, the count as stored within the counter 182 indicative of thepulses derived from the linear encoder 26, is actuated to initiate andto terminate its counting in response to the output of the rotary meterencoder 40, thereby insuring that the count stored in the counter 182accurately corresponds to a count as stored within the programmablecounter 174a, which is indicative of the fluid measurement made by thetest meter 38.

Referring now to FIG. 9F, in step 992 the final values of theaforementioned pressures are obtained after the end of test flag hasbeen set and are converted to a floating point decimal before beingaccumulated and averaged. The final values of pressure and temperatureare outputted via the logic circuit 190a of FIG. 4D to be displayed uponthe CRT terminal 112 in a manner in accordance with the subroutine asdescribed above with regard to FIG. 8P. Next in step 994, the countaccumulated in the counter 182 is converted to a floating point decimalform and in step 620, the servomotor 20 is decelerated to a stop inaccordance with the subroutine 620 discussed above with respect to FIG.8G. Thereafter, step 996 provides command signals via the PI/O circuit196 and logic circuit 194b to actuate the solenoid associated with thesecond exhaust valve 36 to open same and to actuate the solenoidassociated with the first, inlet valve 34 to close the inlet valve. Nextin step 998, the various parameters as have now been finally collectedare used to calculate the volumes as indicated by the output of thelinear optical encoder 26 and the meter rotary optical encoder 40 in amanner that will be explained in greater detail with respect to FIG. 9N.In step 1000, a command is sent to the logic and driver circuit 198a toenergize the test complete indicator 111d and thereafter, in step 1002,the output results as calculated in step 998 are transferred to the hardcopy printer as will be more fully explained with respect to FIG. 9P,and the piston 14 is returned to its lowermost normal, or park positionby step 322, as more fully shown in FIG. 6B. At this point the programreturns to the beginning of step 952a of FIG. 9C to determine whetherrepeated or different flow rate tests are to be made.

In FIG. 9G, the interrupt subroutine 975 is shown and is enteredprimarily when the stop pushbutton 111g is depressed by the operator, orwhen in step 974 of FIG. 9E there has been a determination of failuredue to the combination of an absence of rotary encoder counts, and thepresence of the cylinder at its upper position corresponding to theplacement of the proximity switch 54. Upon pressing the stop button111g, the servomotor 20 is quickly decelerated to a halt and the systemis "locked up" in its stop mode until the primary power is removed andthen reapplied. Upon reapplication of power, the meter prover system 10will return to its standby mode. Under either condition, the programenters via point 975 as shown in FIG. 9G and in step 1004, causes thelogic and driver circuit 198a to actuate a light behind the stoppushbutton 111g. In step 1006, the current motor speed as derived fromthe logic circuit 198b is stored in the speed compare buffer of the RAM126. Next, the servomotor 20 is decelerated in accordance with thedeceleration subroutine 620 as shown in FIG. 8G. Thereafter, step 1008sends commands to the logic circuit 194b to cause the associatedsolenoid to open the second exhaust valve 36 and to actuate theassociated solenoid to close the first, inlet valve 34. At this pointthe subroutine goes into a wait step 1010 until power is removed andthen reapplied.

As shown in FIG. 9H, an Interrupt 1 routine is entered when the operatorpresses the reset button 111g of the system control and status module111 whereby the program being conducted is interrupted and exits to step1012, wherein the logic and driver circuit 198a is controlled toenergize the light behind the reset button 111g. Next in step 1014, thecurrent speed of the servomotor 20 is read via the logic circuit 198band is stored in the speed compare buffer, i.e., an addressable locationof the RAM 126. At that point, the servomotor 20 under the control ofthe logic circuit 194a is decelerated to a stop condition by thesubroutine 620 as shown in FIG. 8G, and the return is made to theprogram via point 212 and in particular to the step 214 as shown in FIG.5.

A third interrupt subroutine, as referred to above with respect to steps976 and 990 of FIG. 9E, is shown in FIG. 9J as automatically implementedat the end of the meter test when the interval timer 174 outputs a pulsevia its logic circuit 177 to the Interrupt 2 input of the CPU 120, thispulse occurring after the down counting of the input of one of thefactors corresponding to one, one-half, or one-fourth cubic foot of thetest volume to be drawn by the meter prover system 10 through the meter38. Initially, the status of the system is stored in step 1018 inappropriate locations within the RAM 126 and in step 1020, the counters174a and 182 of FIG. 4C are disabled and the stored count of the linearcounter 182 is stored in appropriate locations within the RAM 126,before each of the counters 174a and 182 is reset. In step 1024, a oneor flag is disposed within the test over register of RAM 126, upon theoccurrence of the counting down of one of the aforementioned factors orparameters by the counter 174a. Thus, the end of a test may occur midwaybetween the one-second sampling pulses that are used to obtainmeasurements of pressure and temperature. Thus, it is necessary to waitto obtain that final set of measurements of pressure and temperature andthis is done by setting the end of test flag immediately upon theoccurrence of the down counting of the aforementioned factors. The meterprover system 10 will continue to operate to accumulate data asindicated in FIG. 9E until step 990 occurs, at which time the test overregister of the RAM 126 is accessed to see whether a test over flag hasbeen set and if so, then the test is brought to a half. If stillrunning, in step 1028, the status of the system is recalled and themeter prover system operation continues at the point of interruptionwithin the meter test routine as shown in FIG. 9E.

The routine 984 generally indicated in FIG. 9E for inputting the valuesof pressure and temperature is more fully shown in the subroutine shownin FIG. 9K, wherein the initial step 1032, an indication of thedifferential pressure as obtained from the differential pressuremeasuring device 46 is converted into binary data by the A/D converter166 and is stored in a designated location within the RAM 126.Similarly, a differential pressure as measured by the piston pressuretransducer 51 is converted by the A/D converter 166 into binary data andis stored by step 1034 in a designated location of the RAM 126.Similarly, the barometric pressure as measured by the transducer 109disposed in the prover room 106 in which the meter prover system 10 ishoused, is converted by the A/D converter 166 into binary data and isstored by step 1036 in a designated location in the RAM 126. Similarlyin steps 1038, 1040, 1042, the temperature inputs TP1, TP2, TM3, and TM4 from the temperature measuring devices 57, 48, 42, and 44, areconverted to binary data by the A/D converter 158 and are stored withindesignated locations at the RAM 126, before returning to step 986 ofFIG. 9E.

Step 986 as generally shown in FIG. 9E is more fully shown in thesubroutine of FIG. 9L where in step 1046, each of the temperaturescorresponding to the prover temperatures TP1 and TP2, and the metertemperatures TM3 and TM4 is converted from a binary voltage to degreesFahrenheit in a floating decimal format and then is stored in adesignated location within the RAM 126. Next in step 1048, in similarfashion, the binary voltages indicative of the pressures MP1, MP2, andthe barometric pressure PB are taken from their designated locationswithin the RAM 126 and are converted to pounds per square inch (psi) ina floating point decimal format and are restored in designated locationsin the RAM 126, before returning to step 988 as shown in FIG. 9E.

The subroutine or step 988 as shown in FIG. 9E for accumulating andaveraging the test data is more fully shown with respect to thesubroutine shown in FIG. 9M. In step 1050, the digital values of thefirst and second prover temperatures TP1 and TP2 are added together toprovide an Average Prover Temperature (ATP). This value is in turn addedto the accumulated previous values of ATP, thus accumulating a series ofN samples of the Average Prover Temperature during the conducting of ameter test. In step 1052, the meter temperatures TM3 and TM4 are addedtogether to obtain an Average Meter Temperature (ATM) and this new valueis added to the previously accumulated values of the Average MeterTemperature ATM to obtain a quantity indicative of N consecutive samplesof the ATM taken during the course of a meter test. In step 1054, avalue of the ambient or barometric pressure PB is added to the sum ofthe barometric pressure PB plus the differential pressure MP2 takenbetween the ambient pressure and the pressure established within themeter 38 to obtain an Average Meter Pressure (APM). The Average MeterPressure is added to the previously accumulated values of the AverageMeter Pressure to obtain a quantity indicative of N consecutive samplesof the APM taken during the meter test. In step 1056, a value of theambient or barometric pressure PB is added to that differential pressureas obtained from the differential pressure PP1 transducer 51 to obtainan Average Prover Pressure (APP). The Average Prover Pressure (APP) isadded to the previously accumulated values of the Average ProverPressure to obtain a quantity indicative of N consecutive samplings ofthe APP taken during the meter test. In step 1058, the number of samplesof each of the values taken above in steps 1050, 1052, 1054, and 1056 isadded to determine the total number N of samples, whereby in succeedingsteps an average value of each of these parameters may be obtained bydividing the accumulated quantity by the factor N.

Step 998, as shown in FIG. 9F, will now be explained in more detail withrespect to FIG. 9N. As indicated above, the accumulated values ofaverage pressure temperature (ATP), average meter temperature (ATM),average meter pressure (AMP), and average prover pressure (APP) areindicative of N samples taken during the course of the meter test and instep 1060 these average values are obtained for each of the temperaturesand pressures. Next, in step 1062, the percent error of the output ofthe meter encoder 40 of the fluid passing through the meter 38 withrespect to the standard volume passed therethrough as drawn by the meterprover system 10 is calculated in accordance with the indicatedequation. The values of meter pressure PM, prover pressure PP, provertemperature TP, and meter temperature TM are those averaged values asdetermined from step 1060, whereas the prover volume count K wasobtained as an indication of the accumulated counts that was produced bythe linear encoder 26 and accumulated within the counter 182, thesecounts being indicative of a selected standard volume, e.g., one cubicfoot, one-half cubic foot, or one-fourth cubic foot. As shown in FIG.9N, the ratios of PM to PP, and TP to TM provide, respectively, pressureand temperature correction factors. As explained above, there existsdifferences of fluid temperature and fluid pressure between the fluidwithin the meter prover 10 and the fluid meter 38 under test. The notedratios as determined by step 1062 provide appropriate correction factorswhereby the differences in temperature are compensated for to give anaccurate indication of percent error of the meter reading of fluidvolume with respect to that calibrated indication or reading provided bythe meter prover 10. The factor K* is representative of those counts asstored in the programmable counter 174a indicative of the fluid flow asmeasured by the meter 38. As shown in step 1062, the factor K* ismultiplied by a constant C to convert the count, e.g., 40,000 for onecubic foot, to a value of the volume to be drawn through the meter 40.In the illustrative example, where the factor K* as entered into theprogrammable counter 174a is 40,000, the constant C is chosen as1/40,000. Further, the number of counts as derived from the linearencoder 26 and counted by the counter 182 is multiplied by a calibrationfactor which, as will be explained later in detail, is derived byaccurately measuring the volume of the chamber 28 of the meter prover 12and correlating the precisely measured volume to the series of pulsesoutputted by the linear encoder 26. In an illustrative example of thisinvention, for a selected volume of one cubic foot of the chamber 28, itwas determined that 38,790 output pulses were derived from the linearencoder 26. Thus, the calibration factor would be selected as inverse ofthis count or 1/38,790. In similar fashion, if a different volume was tobe drawn through the meter 38 and the programmable counter 174a was tobe programmed with a count corresponding to a different flow, it wouldbe necessary to determine a different calibration factor correspondingto that volume as defined within a selected region of the chamber 28. Inpractice, the count of 38,790 is obtained empirically by moving thepiston 14 along a length of the chamber 28 corresponding to preciselyone cubic foot and calculating or otherwise determining the number ofpulses as outputted by the linear encoder 26. Similar measurements andencoding will be taken empirically to determine the counts for one-halfand one-fourth cubic feet flow corresponding to the output of the linearencoder 26 as the piston 14 is moved distances from the start-testposition along the cylinder 12 corresponding illustratively to one-halfcubic foot and to one-fourth cubic foot volumes within the cylidner.Thus, the actual counts and therefore the corresponding calibrationfactors for one-half and one-fourth cubic feet will correspond preciselyto these volumes as defined by the cylindrical wall of chamber 28. Inthis manner, a calculation of the percent error between the reading ofthe meter 38 and the actual volume as drawn into the chamber 28 can bemade with great accuracy, by the use of calibration factors that havebeen determined in accordance with the precise volume of thecorresponding regions of the cylindrical wall of the chamber 28. Afterthe step 1062 has been executed, the program returns to the next step1000 as shown in FIG. 9F.

The calculation of the average temperatures and pressures as generallydisclosed in step or subroutine 1060 of FIG. 9N is more completely shownby the subroutine as set out in FIG. 9Q, as previously indicated in step1050, each measurement of temperature is added to the previousmeasurement to obtain a total indicative of accumulated discretemeasurements of prover temperature ATP during the course of a singletest. As indicated in step 1064 as shown in FIG. 9Q, this accumulatedvalue of ATP is divided by the number of samples AVCTR=N+2 and added to459.67 to provide the final averaged temperature FTP of the prover indegrees Kelvin. In similar fashion in step 1066, the value of thetemperatures TM3 and TM4 are added successively to each other during thecourse of the meter test to provide an accumulated value of the averagetemperature ATM of the meter during the course of the test, and the ATMis divided by the number of samples or counts of the one-second samplingclock which is in turn added to 459.67 to give a final averagetemperature FTM in terms of degrees Kelvin. In similar fashion, in step1068, the accumulated values of the average pressure APM of the meter asaccumulated during the test is divided by the number AVCTR of samplestaken during the test to provide a final FPM of the meter in terms ofpounds per square inch absolute. In step 1070, the accumulated values ofthe average prover pressure APP as accumulated during the course of themeter test are divided by the number AVCTR of samples to provide anindication of the final pressure of the prover FPP in terms of poundsper square inch absolute, before returning to the next step 1062 asshown in FIG. 9N.

The accuracy of the meter prover 10 to measure the volume drawn throughthe meter 38 is dependent and is limited by the variations in themeasurements of fluid pressure and temperature during a meter volumetest. The variations in fluid pressure and temperature as occur during ameter volume test run are greater than those variations that may occurin the measurement and calibration of the volume of the meter prover.Thus in general, the actual volume of fluid delivered through the meter38 as the piston 14 is moved from a first to second position may beapproximated by the following expression:

    V≈(V.sub.1 -V.sub.2)[1+(δT/T.sub.1)-(δP/P.sub.1)]+V.sub.2 [(ΔT/T.sub.1)-(ΔP/P.sub.1)]

where V₁, P₁, and T₁ are respectively the initial volume, fluid pressureand temperature existing within the chamber 28 of the prover 10 at thebeginning of a meter volume test run, ΔP and ΔT are the correspondingchanges in pressure and temperature that occur during the test, and δTand δP are the mean deviations from T₁ and P₁ at the fluid meter 38. Asexplained above, the logic circuit 178 as shown in FIG. 4C provides aone-second clock signal that samples the output of the temperaturetransducers 42, 44, 48, and 57, as well as the pressure transducers 46and 51 to provide samples of these variables throughout the volume metertest run. As discussed above, the periodic samples of the metertemperature TM3 and TM4, and the prover temperature TP1 and TP2 asobtained in step 984 of FIG. 9E are summed in steps 1050, 1052, 1054,and 1056 of FIG. 9M together to obtain a spatially averaged metertemperature and prover temperature, which are time averaged by beingsampled and summed over the test run as explained with respect to steps1064, 1066, 1068, and 1070 of FIG. 9Q. In this manner, the continuouschanges in both pressure and temperature are measured at the fluid meterand the prover 10. By so averaging in a spatial and time sense, thevariations in temperature and pressure that would otherwise cause anerror in the calculation of the change of volume may be avoided.Temperature changes in the fluid as drawn into the meter prover ascaused by adiabatic expansion across a pressure drop of 1.5"H₂ O can beas large as 0.5° F., causing an error in the calculation by as much as0.1%. Thus, it is necessary to monitor accurately the fluid pressure andtemperature throughout the system and apply the necessary corrections inorder to obtain the "true" volume drawn into the meter prover 10. For anaccuracy of 0.05% in volume, the parameters δT and δP between thechamber 28 and the meter inlet need to be monitored to an accuracy ofbetter than ±0.1° F. and ±0.05"H₂ O, respectively. The temperaturetransducers and pressure transducers described above with respect toFIG. 1 have such a capability to achieve the desired accuracy fortemperature and pressure measurement and provide the desired accuracy inthe measurement of the volume.

Step 1002, as shown in FIG. 9F as outputting the results of theconducted tests upon the meter 38 to the hard copy printer, is morefully shown in FIG. 9P. In the first step 1072, the printer is strobedby the logic 190b to initialize its operation and thereafter the percenterror as calculated previously in step 1062 is printed out upon theprinter. Next, in step 1074, a line feed command is applied for theprinter to advance its paper by one line, before in step 1076, the flowrate at which the test was conducted is displayed in step 1076. In step1078, ten line feed command signals are applied to the printer to feedthe paper ten lines before returning to step 322 in FIG. 9F.

A significant aspect of this invention resides in the method ofaccurately measuring the volume of the chamber 28 of the cylinder 12 andto use that measurement to accurately calibrate the output of the linearencoder 26 to provide a manifestation of volume per pulse output of thelinear encoder 26. As indicated in FIG. 2A, the linear encoder includesa scale 24 with a high number of accurately, closely spaced markings102, whereby the optical encoder 26 provides a train of output pulsescorresponding to the passage of each such marking past the opticalencoder. By accurately correlating the number of such output signals tothe precisely determined volume of the chamber 28, the linear encoder 26may be encoded with a corresponding high degree of accuracy to therebyimprove the calibrated indication of meter registration or error of themeter 38 under test.

In such a calibration procedure, it is first necessary to measure thevolume of the chamber 28 with great accuracy. A method of volumemeasurement is employed including the establishing of a high frequency,electromagnetic field within the cavity; the principles of suchmeasurement method will now be explained. The inside dimensions of theregularly shaped chamber 28 completely surrounded by conducting wallscan be accurately determined by measuring the frequencies at whichresonant conditions occur for the electromagnetic field establishedwithin the chamber 28. For a given geometry, the electromagnetic fieldswithin the chamber 28 can assume a variety of spatial configurations. Atdiscrete frequencies, the electromagnetic energy confined within thechamber 28 is stored over time intervals long compared with its waveperiod and these resonant solutions are designated as the normal modesof the chamber 28. The ratio of the energy stored to that dissipated percycle of the resonant frequency is defined as the quality factor or "Q"of the resonance. The quality factor Q is a measure of the dissipativelosses due to the ohmic resistance of the walls to the electricalcurrents induced by the electromagnetic fields. For a given normal mode,the resonant frequency is uniquely determined by the dimensions of thechamber 28 and the propagation velocity of light in the medium fillingthe volume. Consequently, by simultaneously measuring the resonantfrequencies of a number of normal modes equalling the linear dimensionsspecifying the volume (one for a sphere, two for a right circularcylinder, and so forth), the volume of the chamber 28 can be determinedto an accuracy comparable to the precision of the frequencymeasurements.

For a given chamber geometry, there is an infinite set of normal modeswhose resonant frequencies will have a lower bound value correspondingto a free-spaced wavelength of the order of the linear dimensions of thechamber 28, but no upper bound. A volume change caused by a mechanicaldisplacement of one of its linear dimensions will, in turn, change theresonant frequency of the low ordered modes by approximately the samefraction.

Briefly, as shown in FIG. 10, means in the form of the antenna 70 isprovided to establish or generate an electromagnetic field within thechamber 28 and to extract therefrom a relatively small portion of thestored electromagnetic energy to be measured by the circuit of FIG. 10.As will be explained in detail later, measurements are made to determinethe frequencies f at which resonance occurs within chamber 28. Theselection of the configuration of the chamber 28 is significant for ifan arbitrarily shaped chamber is used, the mathematical relationshipbetween the resonant frequencies f and the dimensions of such a chambermay have no closed or analytical solution. Thus, the chamber 28 isselected to be of a regular geometry to assure that the dissipatedlosses and the effects of coupling are negligible and to provide knownMaxwell equations defining the relationship between the chamberdimensions and the resonant frequencies subject to the boundaryconditions that the electrical field E be radial and the magnetic fieldH be tangential to the totally enclosed surfaces of the regularly shapedchamber 28. Under these conditions, the field solutions for the chamber28 will take on a relatively simple form and recognizable perturbationscan be predicted.

Thus, in a preferred embodiment of this invention, the chamber 28 isselected to be a right circular cylinder as is formed by the innersurface of the cylinder 12, the head 60, and the exposed surface of thepiston 14. It is recognized that a chamber 28 of such a configurationpermits the piston to be driven therethrough to displace a known fluidvolume, as explained above. The normal modes of the electromagneticfield established in the chamber 28 being configured as a right circularcylinder are divided into two general classes: the transverse electricmodes (TE) for which the electric field is zero along the cylindrical(z) axis of the chamber 28, and the transverse magnetic modes (TM) forwhich the magnetic field is zero along its cylindrical axis. They arefurther specified by three integers l, m, and n, which are defined forthe TE modes in terms of the cylindrical coordinates, r, θ, and z by:

l=number of full-period variation of E_(r) with respect to θ;

m=number of half-period variation of E.sub.θ with respect to r;

n=number of half-period variation of E_(r) with respect to z.

A similar set of indices exists for the TM modes for which the integersl, m, n are correspondingly defined in terms of the components of themagnetic field; H_(r) and H.sub.θ.

The solutions for the resonant frequencies of the normal modes areexpressed in terms of the geometrical dimensions and roots of Besselfunctions by the geneal expression: ##EQU2## where D is the diameter, Lis the length, c is the speed of light in the medium filling the cavityvolume and x_(lm) are given respectively by:

x_(lm) =m^(th) root of J'_(l) (x)=0 for the TE-modes,

x_(lm) =mth root of J_(l) (x)=0 for the TM-modes.

Numerical values for these Bessel roots corresponding to the variouslower ordered TE and TM modes are taken from the following table:

    ______________________________________                                        Transverse Electric Modes                                                                      Transverse Magnetic Modes                                    (TE)             (TM)                                                         TE        x.sub.lm   TM         x.sub.lm                                      ______________________________________                                        11        1.84118    01         2.40483                                       21        3.05424    11         3.83171                                       01        3.83171    21         5.13562                                       31        4.21009    02         5.52008                                       41        5.31755    31         6.38016                                       12        5.33144    12         7.01559                                       ______________________________________                                    

A plot of the quantity (fD)² vs (D/L)² of equation 1 is a straight linewith intercept (cx_(lm) /π)² and slope (cn/2)². Such a mode chart isshown in FIG. 13 for the lower modes of the right cylindrical chamber 28for values of n up to 2. FIG. 13 shows graphically the relative resonantfrequency values as a function of the geometric parameter (D/L)² and thevariation in resonant frequencies as the linear dimension L is changed.It is also useful in predicting the number of resonances expected to beencountered in a given frequency range for any fixed D/L ratio as wellas the values of L at which two difference modes are degenerate infrequency, and hence would interfere with each other.

The mode chart of FIG. 13 is used to determine the modes ofelectromagnetic field excitation, the expected resonant frequencies ofthe selected modes, and the dimension in terms of the diameter D andlength L of the chamber 28. In an illustrative embodiment of the chamberas shown in FIG. 10, the diameter D is set equal to 12" and thevariation in the length L is from 10" to 30". Consequently, thecorresponding values of (D/L)² have the range of values from 1.44 to0.16. If the frequency range of observation is between 500 MHz to 1000MHz, then (fD)² will vary between 2.32×10²⁰ and 9.29×10²⁰ (cycles/sec)²cm². The number of resonant modes expected to be encountered over thevariation in length L for this configuration between the range of 500 to1000 MHz is then just given by the number of lines included in therectangle shown on the mode chart of FIG. 13. As can be seen, at L=10",there are only three modes which occur between 500 to 1000 MHz. Theseare, namely, the TM₀₁₀ mode occurring at approximately 755 MHz, theTE₁₁₁ mode occurring at 830 MHz and the TM₀₁₁ mode occurring at 960 MHz.On the other hand, for L=30", there are eight modes, namely TE₁₁₁,TE₁₁₂, TM₀₁₀, TM₀₁₁, TM₀₁₂, TE₂₁₁, TE₂₁₂, and TE₁₁₃ which for purposesof clarity, are not shown in FIG. 13. At any intermediate position, thenumber of modes and their resonant frequencies f can be obtained fromthe intersection of the vertical line corresponding to the desired(D/L)² value with the lines designating the various modes. Since themeasurements of the resonant frequency of any two distinct modesuniquely specify both D and L, the other modes may be used either as aredundancy check on the measurements or as a means for evaluating theeffects of perturbation caused by deviation of the geometry from theidealized case as well as any higher ordered correction terms which maybe present.

In a qualitative sense, it is understood that the electric and magneticfield components of the electromagnetic field are perpendicular to eachother and have a defined relation at a resonant frequency to thedimensions D and L of the chamber 28 of a regular geometry and inparticular the diameter and length of the chamber 28, as shown in FIG.10. As will be explained, the relationship between the resonantfrequency and the dimensions D and L for a particular mode can berelated by a mathematical expression. The chamber 28 having a rightcircular cylinder configuration has two unknown dimensions that defineits volume, i.e., its diameter D and its length L. Thus, it is necessaryto provide two mathematical expressions that may be solvedsimultaneously for the unknown values D and L, and therefore it isnecessary, as indicated above, to establish electromagnetic fieldswithin the chamber 28 of two distinct modes and obtain the resonantfrequencies of these two modes whereby the values of D and L and thusthe volume of the chamber 28 may be calculated. As will be explained,the modes of excitation are selected to determine resonant frequencieswith correspondingly high quality factors whereby the effects ofperturbations to introduce errors into the measurement of D and L may beminimized.

The TM₀₁₀ mode line has zero slope, as shown in FIG. 13, and istherefore independent of the dimension L of the chamber and is only afunction of the diameter. This unique property can therefore be used toidentify this mode in experimental measurements. The TM₀₁₀ mode ofexcitation can be used to obtain an independent measurement of thedimension D. Furthermore, it can be seen that the rate of change of theresonant frequency for any given mode as a function of the dimension Lis solely determined by the last index n. Consequently, the frequenciesof the modes such as TE₁₁₁, TM₀₁₁, and TE₂₁₁ will shift by the sameamount as L is varied whereas the TE₁₁₂, TM₀₁₂, and TE₂₁₂ modes will allshift together at twice the rate. Consequently, the tuning properties ofthese modes can be used to determine the relative change in the length Lto very high accuracy once the absolute diameter of the cavity has beendetermined.

The quality factor or Q of the chamber 28 at resonance as excited in agiven normal mode is important in two respects. First, it determines thesharpness of the resonant frequency response and therefore limits theultimate accuracy with which the resonant frequency can be measuredexperimentally. More important, the quality factor Q is a measure of theorder of magnitude of the expected deviation of the resonant frequencyfrom the idealized results as given by equation 1. In general, thehigher the Q for a given mode, the more accurate the theoreticalexpressions are in terms of determining the geometrical dimensions ofthe cavity. Thus, the modes for exciting the chamber 28 are selected toprovide the highest quality factors Q, and thus provide the moreaccurate determination of the dimension and thus the volume of chamber28.

For a volume comprised of perfectly conducting walls, the unloaded orintrinsic Q_(o) of the chamber is infinite and the frequency solutionsto the resonant normal modes are exact. For walls of finite resistivity,the electric and magnetic fields within the chamber 28 penetrate intothe walls to a distance defined as the skin depth δ, which is given bythe expression

    δ=[λρ/120π.sup.2 μ].sup.1/2 cm      (2)

where μ is the permeability of the wall material, λ is the free-spacewavelength in cm, and ρ is the resistivity (d.c.) of the walls inohm-cm. Since a finite skin depth makes the apparent dimensions of thechamber as seen by the electromagnetic fields somewhat larger than theactual geometrical dimensions, the dissipative effect caused by theohmic losses on the walls perturbs the resonant frequency of the normalmodes and shifts them to a lower value. A measure of this perturbationis the value of the ratio of the skin depth to the free-space wavelengthor (δ/λ), which can be calculated via equation 2 by using known valuesof the d.c. resistivity and permeability of the wall material. For acavity made of copper (μ=1,ρ=1.72×10⁻⁶ ohm-cm), the skin depth is equalto 3.8×10⁻⁵ λ^(1/2) cm. At 1000 MHz (λ=30 cm), the ratio (δ/λ) isapproximately equal to 7×10⁻⁶. This correction to the resonant frequencycaused by the finite conductivity is clearly negligible for the presentapplication. For series 300 stainless steel, (μ=1,ρ=72×10⁻⁶ ohm-cm), theraio of (δ/λ) at 1000 MHz is 4.5×10⁻⁵ which is becoming non-negligiblecompared to to the desired overall accuracy of 0.01% in absolute volumeaccuracy. In a preferred embodiment, the walls of the chamber 28 arechrome-plated, (μ=1,ρ=13×10⁻⁶ ohm-cm), the corresponding value of (δ/λ)is equal to 2×10⁻⁵ at 1000 MHz. Consequently, on the base of theoreticalcalculations, the correction to the resonant frequency of the normalmodes in the chamber 28 of a right circular cylinder configurationshould be negligible and the expression given by equation 1 should beadequate in giving an overall volume determination to an accuracy betterthan 0.01%.

In practice, however, the theoretical skin depth value for a givenmaterial is never achieved due to a variety of reasons, including wallimperfections, material impurities, and residual surface contaminations.Consequently, it is necessary to experimentally determine the effectiveskin depth by measuring the Q of the chamber 28 to selected of thepreferred modes of excitation, and if necessary, apply the appropriatecorrection to the volume determination due to this effect.

The expression Q_(o) of the chamber 28 is obtained by evaluating theratio of the energy stored to the dissipative losses occurring on thewalls per cycle of the electromagnetic oscillation, which can be writtenas, ##EQU3## where H is the normal mode magnetic field vector and δ isthe skin depth. The Q factors in terms of the normal modes andgeometrical shape for the chamber 28 of a right cylindrical cavity aregiven by the following expressions: ##EQU4## where R=(D/L), P=nπ/2 andall other symbols are as previously defined.

By evaluating the right hand sides of the above expressions for a givenmode and cavity geometry and dividing it by the experimentallydetermined Q, an effective δ/λ can be obtained. A direct comparison ofthe result obtained with the calculated via equation 2 then gives aquantitative evaluation of the magnitude of the perturbation expected inthe volume determination of the chamber 28.

The chamber 28 is coupled to an external measurement circuit as shown inFIG. 10 whereby microwave power is introduced into the chamber 28 toestablish an electromagnetic field therein and to extract reflectedpower therefrom. The chamber 28 is a reflection type cavity requiringonly one coupling device in the form of the antenna 70. As will beexplained in detail later, the resonant characteristic, and inparticular the resonant frequency of a given normal mode, is determinedby measuring the power reflected from the antenna 70 as a function ofthe incident microwave frequency. The use of a reflected type chamber 28permits minimal perturbation from an idealized cavity response andpermits an implementation by the use of a directional coupler 1106 whichallow sampling of the reflected power without interference from theincident power. As shown in FIG. 10, the power output of a sweepgenerator 1100 is applied to excite the atenna 70 while the reflectedpower may be transferred by the coupler 1106 to a crystal detector 1110.

The presence of the coupling device in the form of the antenna 70introduces an additional loss term in the dissipation of the resonantelectromagnetic energy stored within the chamber 28, namely, the amountof power extracted for measurement. This is usually defined as anequivalent coupling Q or Q_(c) as distinguished from the "unloaded" Q ofthe cavity or Q_(o). In addition, the interaction of the cavity with therest of the circuits of FIG. 10 via the antenna 70 need to be taken intoaccount in order to derive an accurate description of the"cavity-coupling" system for evaluating the appropriate expressions inthe present invention.

It can be shown that for a reflection-type chamber 28, i.e., a chamberfor which power is introduced and extracted by a single antenna 70, theratio of the reflected power to the incident power near a resonance isgiven by the expression, ##EQU5## where ν is the frequency, ν_(o) is theresonant frequency, Q_(o) is the unloaded Q of the cavity resonance, andQ_(c) is the coupling Q which is proportional to the power loss throughthe coupling device.

At the resonant frequency ν_(o), the ratio of the reflected power to theincident power is defined as the reflection coefficient for the givennormal mode, i.e.

    (P.sub.r /P.sub.o).sub.ν=ν.sbsb.o =β=(Q.sub.c -Q.sub.o).sup.2 /(Q.sub.c +Q.sub.o).sup.2                                 (7)

For β=0, the cavity is considered to be 100% coupled and Q_(o) =Q_(c).This condition corresponds to the low-frequency equivalent circuit casewhere the load impedance is matched to the generator impedance.

Combining equations 6 and 7, and eliminating Q_(c), the unloaded Q_(o)of the normal mode is given in terms of the measurable parameters by,

    Q.sub.o =ν.sub.o [(P.sub.r /P.sub.o)-β/1-(P.sub.r /P.sub.o)].sup.1/2 /(ν-ν.sub.o)(1+β.sup.1/2)   (8)

Therefore, by measuring β and the frequency width at some arbitrarypower level (P_(r) /P_(o)) on the cavity resonant response curve, thequantity Q_(o) can be determined. If a "half-power" point is definedsuch that

    P.sub.1/2 =(1+β)/2,                                   (9)

then the frequency difference corresponding to the two half-power pointsis known as the "half-width" of the resonant response and is given by

    Δν=2(ν.sub.1/2 -ν.sub.o)

where ν_(1/2) is the frequency corresponding to the half-power points.For this case, equation 8 further reduces to,

    Q.sub.o =(2ν.sub.o /Δν)/(1+β.sup.1/2).    (10)

The value of Q_(o), therefore, varies between (ν_(o) /Δν) and (2ν_(o)/Δν), depending on the degree of coupling.

A pictorial representation of the chamber response curve, together withthe defined parameters, is shown in FIG. 14. The center frequency of theresponse, ν_(o), corresponding to a minimum of the reflected power, isthe resonant frequency of the normal mode.

It is understood that the frequency measuring circuit as shown in FIG.10 effects a change of the resonant frequency, i.e., frequency pulling,caused by the interaction between the chamber 28 with the elements ofthe circuit of FIG. 10. In the circuit as shown in FIG. 10, wherein thefrequency of the sweep generator 1100 is varied by a factorapproximately 2, the directional coupler 1106 receives the output powerof the sweep generator 1100 and applies a relatively small portionthereof to the antenna 70. In particular, the power applied to theauxiliary or output port of the directional coupler 1106 isapproximately 80% of the output of the sweep generator 1100. The chamber28 is connected to the main input port, and the crystal detector 1110 isconnected to the third port of the directional coupler 1106 to measurethe microwave power reflected from the chamber 28. The use of thedirectional coupler 1106 results in a factor of 100 attentuation or"padding" between the sweep generator 1100 and the load as imposed bythe antenna 70. As a result, the sweep generator 1100 is respectivelyisolated from the antenna 70, i.e., the coupling system, to insure thatno interaction occurs to perturb the chamber response. As a result ofthe isolation imposed by the coupler 1106 between the antenna 70 and thegenerator 1100, the amount of frequency pulling is determined by thequality factor Q of the chamber 28, the coupling coefficient β, and theVSWR between the crystal detector 1110 and the cavity coupling system.Assuming that the sweep generator 1100 is totally decoupled from thecavity 28, a cavity 28 having a quality factor Q of 5,000, a couplingcoefficient β of 0.5 and a residual VSWR of 2, will provide a frequencypulling in the order of 1.3×10⁻⁵ or 0.0013%. This deviation is an orderof magnitude better than required to achieve desired overall measurementof the chamber volume to an accuracy of better than 0.01%.

Further, an analysis of the cavity 28 and its associated resonantfrequency measuring system, as shown in FIG. 10, have shown thatperturbations due to distortions in the geometry of the chamber 28whether due to the out of roundness of the cylindrical shape of thecavity 28 or to small localized surface irregularities and deformations,indicates that such perturbations can be compensated for by taking thefollowing precautions. First, if the machine tolerence of the chamber 28is such that the diameter D of its cylindrical configuration ismaintained to within the limits of 12 mills out of roundness, then thediameter D and thus the volume of the chamber 28 can be determined withan accuracy in the order of 10⁻⁵ or less and, thus, such deformation maybe neglected for the present method of measuring volume. Similarly, theshift in the chamber resonant frequencies for any normal mode caused bya small inward or outward dent on the interior wall of the chamber 28 isdeemed negligible is the hole dimension is well below the cut-offwavelength of the electromagnetic field established within the chamber28 and the hole does not couple electromagnetic field to anotherstructure; under these conditions, the frequency pulling will beapproximately proportional to the ratio of the cube of the hole diameterto the volume of the chamber 28. Thus, as a practical matter, thefrequency pulling for inward or outward dents in the walls of thechamber 28 is negligible; for example, a 1 inch diameter hole as placedwithin a chamber 28 having a diameter of approximately 12 inches andlength of 20 inches will provide a change of the resonant frequency byonly 7 parts in 10⁵.

Considering the effect of the inlet 62 as well as the openings toreceive the transducers 51 and 57 within the piston 14, these openingsor holes may be filled with metallic plugs during the volume measurementand calibration to virtually eliminate these sources of error fromeffecting the determination of the resonant frequency.

In order to satisfy the accuracy requirement of ±0.01% in themeasurement of the displacement volume of the chamber 28, the resonantfrequency measuring circuit as shown in FIG. 10 should be capable ofmeasuring the resonant frequencies of the normal modes as establishedwithin the chamber 28 to 1 part in 10⁵. The circuit, as shown in FIG.10, is designed to reduce systematic error which can effect themeasurement of the resonant frequencies f, such distortions due toimpedance mismatch between the sweep generator 1100 and the antenna 70,variations and fluctuations of the microwave power, extraneous noise,and sensitivity to component drifts. As shown in FIG. 10, the microwavepower source takes the form of the sweep generator 1100 which mayillustratively take the form of that generator manufactured by Texscanunder their model disignation VS80A. The sweep generator 1100 may beoperated illustratively at a fixed frequency (CW) or automatically tosweep through a range between 50 KHz and 300 MHz at a rate set between0.05 Hz and 30 KHz. In addition, the output of the sweep generator 1100may be controlled by its vernier knob 1100a to sweep at an operatorcontrol change of frequency through the noted range. The output of thesweep generator 1100 is applied by a coaxial cable to a directionalcoupler 1102 which acts as a transformer whereby a portion of the energyapplied across the coupler 1102 is transferred to a frequency counter1108, which in an illustrative embodiment of this invention may take theform of that counter manufactured by Fluke Corporation under their modeldesignation No. 1920A. As will be explained later, the counter 1108displays the frequency at which a standing wave is established withinthe chamber 28. In turn, the output of the coupler 1102 is applied by asimilar coaxial cable to a second coupler 1104 and in turn via thedirectional coupler 1106 to be applied to the microwave antenna 70. Asshown in FIG. 10 and in more detail in FIG. 2A, the microwave antenna 70is a simple metallic loop 70a and is insulated by an insulator 70b fromthe head 60 of the chamber 28.

As is well known in the art, the energy reflected through the antenna 70from the chamber 28 upon occurrence of a standing wave decreasessignificantly in comparison to that enery reflected at otherfrequencies. This is known as the resonance condition, and theassociated frequency as the resonant frequency. Thus, as the frequencyof the output of the sweep generator 1100 is varied, as resonantfrequency is selected at which a standing wave occurs within the chamber28 dependent upon the configuration and dimensions of the chamber 28.The frequency at which the standing wave is established determines, aswill be explained, the chamber dimensions in terms of the diameter D andthe length L, and therefore the volume of the chamber 28. To detect thepower drop at the resonant frequency, the coupler 1106 is connected tothe crystal detector 1110, which converts the microwave power reflectedthrough the antenna 70 to a d.c. signal. In turn, the crystal detector1110, which may illustratively take the form of a Hewlett Packardcrystal detector Model No. 423A (NEG), applies its d.c. output to the Yinput of an oscilloscope 1112. The oscilloscope 1112 may illustrativelytake the form of a Textronix oscilloscope manufactured under their ModelNo. T922R. The X input to the oscilloscope 1112 is provided by the sweepgenerator 1100, so that when the generator 1100 is set in the sweepmode, the reflected power response of the chamber 28 is a function ofthe input signal frequency and is displayed upon the oscilloscope 1112.As seen in the expanded display 1112a, the power reflected through theantenna 70 dips to a minimum 1113, at the resonance frequency in amanner shown in FIG. 14. The frequency at which the minimum 1113 occursis displayed upon the counter 1108. The second coupler 1104 appliesmicrowave power to a crystal detector 1114 which provides acorresponding d.c. signal to be amplified by an operational amplifier1115 and applied to the sweep generator 1100 to provide a level controlupon the output of the sweep generator 1100, whereby substantially aneven power drain is placed upon the sweep generator 1100 as it sweepsthrough that frequency at which a standing wave occurs.

The circuit of FIG. 10 is operated in the following fashion to obtain ameasurement of the resonant frequency. First, the sweep generator 1100is set for wide sweep to permit essentially all of the normal moderesonances to be displayed simultaneously on the screen of theoscilloscope 1112 whereas the resonant response for any particular modecan be displayed individually by an appropriate choice of sweep widthand sweep center frequency. Unambiguous identification of the modes canbe made by measuring their resonant frequencies for a particular settingof the piston position within the chamber 28, and using equation 1, oralternatively, by moving the piston position and comparing the rate ofchange of their resonant frequencies as a function of piston positionwith those shown in FIG. 13.

The resonant frequency f of any given mode is measured by firstdisplaying the response curve on the oscilloscope screen and thenswitching the sweep generator 1100 to its CW mode and manually tuningthe fine frequency knob 1100a until the voltage displayed on theoscilloscope 1112 is a minimum. The display on the frequency counter1108 when this minimum is reached is then the resonant frequency of thecavity normal mode. As a convenience, the second beam of theoscilloscope 1112 can be used to better define the position of thisminimum by setting the system in the sweep mode and manually changingthe vertical position of the second beam so that it just touches thebottom of the resonant response curve. When the generator 1100 isswitched to operate in its CW mode, the resonant frequency f of thechamber 28 is then the frequency setting of the generator 1100corresponding to condition when the two beams coincide. In a preferredembodiment, by simultaneously reading the frequency counter output whilethe two beams are exactly coincident, the effect due to frequency driftsof the generator 1100 is eliminated so that the measurement can be madeto a much higher degree of accuracy than the inherent stability of thesweep generator 1100. In addition, since the measurement depends only onestablishing the minimum in the chamber response curve, it isindependent of non-linearity in the response of the detector 1100 aswell as fluctuations in the incident microwave power with time. Repeatedmeasurements on a given mode indicate that resonant frequency of thechamber 28 can be determined to an accuracy better than ±3 KHz orapproximately 5 parts in 10⁶.

Now, a first embodiment of the method for precisely measuring the volumeof a section of the chamber 28 will be explained in greater detail.Generally, the method of this invention involves measuring the resonantfrequencies of the chamber 28 for two different modes of excitation. Asan example, consider the right cylindrical chamber 28, and measure theresonant frequencies in the TM₀₁₀ and TE₁₁₁ modes. Both modes arenon-degenerate and their resonant frequencies can be determined to anaccuracy of 1 part in 10⁷ or better with standard techniques. The TM₀₁₀mode (parallel plate mode) is dependent only on the average diameter (D)of the chamber 28 and is independent of the cavity height (L), whereasthe TE₁₁₁ mode is dependent on both (D) and (L). Therefore, from themeasurement of the two frequencies, the volume of the chamber 28 can bedetermined. For the case of TM₀₁₀ mode: ##EQU6## where D=diameter, X₀₁=1st Bessel root or J_(o) (X)=0 For the case of TE₁₁₁ mode: ##EQU7##where D=diameter, L=length or height of cavity, X₁₁ =1st root of J'₁(X)=0. Combining the 2 results give ##EQU8##

In terms of the resonant frequencies, the results can be expressed as:##EQU9## where X'₁₁ =1.8412, X₀₁ =2.4048, and c=speed of light in themedium filling the cavity, (air for the present application).

In terms of the total volume of the chamber, ##EQU10## As can be seen,the volume is, to first order, proportional to λ³ or 1/f³. Therefore##EQU11## Hence, the frequencies can be measured accurately to 1 part in10⁷ as by the counter 1108, and thus the theoretical accuracy for v isof the order of 3 parts in 10⁷.

The method can be used to continuously measure the change in volume of aright circular cylinder 12 caused by a positive displacement of itspiston 14. Both the volume of the chamber 28 before and after the pistonmotion, as well as the rate of change of volume can be measured in asimple manner. For the arrangement shown in FIG. 10, as the piston 14moves from position X to position Y, the TM₀₁₀ mode resonant frequencywill remain constant (or change slightly due to non-uniformity in thediameter of the cylinder) and the TE₁₁₁ mode resonant frequency willshift by an amount proportional to the displacement ΔL. At position X,the resonant frequencies f₁ and f₂ are measured and are inserted withinequation 2 to provide an indication of a first volume V₁. Thereafter,the piston 14 is moved to a second position Y and a second set ofresonant frequencies f₁ ', f₂ ' for the modes TM₀₁₀ and TE₁₁₁,respectively, are taken and a second volume V₂ is calculated inaccordance with equation 15. Finally, a displacement volume ΔV iscalculated by subtracting the first determined volume V₁ as determinedat position X from the value V₂ of the second volume as determined atposition Y. In addition, by continuously monitoring the TM₀₁₀ resonantfrequency, the variation of the diameter of the chamber 28 (due tomachining imperfections) between L₁ and L₂ can be measured as a functionof L. In a similar manner, the rate of change of volume can be measuredby continuously monitoring the resonant frequency of the TE₁₁₁ mode.

Perturbations to the above relationships include dielectric propertiesof air, the presence of coupling conduits 30 and 32, and the other gasinlet 62, surface irregularities, finite electrical conductivity of thewall material of the chamber 28 and degeneracy due to mode crossing. To1st order, so long as the irregularities are small compared to λ (whichwill be on the order of 30 cm or larger), the perturbations will beproportional to the volume change. Hence, the method will average overdeformities and give a measurement which will be proportional to thetrue volume of the chamber 28.

The coupling conduits 30 and 32 and gas inlet 62 are made with sizeswell below the cut off wavelength of the microwaves and should perturbthe resonant frequency at most by 1 part in 10⁵ and can be corrected forin the 1st order.

Similarly, the perturbation due to the finite electrical conductivity ofthe wall material of the chamber 28 should be of this same order ofmagnitude if the walls are fabricated or plated with a high-conductingmetal such as copper, silver, gold, or aluminum, and reasonable care istaken in polishing. As an example, the theoretical skin-depth for copperat 300 Mc/s is 3.8×10⁻⁴ cm. The perturbation on the volume is of theorder of the ratio of the skin-depth to the linear dimension of theresonant cavity which, for a right circular cylinder with a radius of 50cm, is approximately 7.6×10⁻⁶. The actual skin depth can be estimatedfrom the dissipative losses in the cavity which are directly related tothe quality factor or Q of the chamber, which can generally beexperimentally measured to about 1% accuracy. Consequently, a firstorder correction can be applied which will reduce the uncertainty tobetter than a few parts in 10⁷.

The resonant frequency change between vacuum and air in the cavity isgiven by,

    (f.sub.vacuum /f.sub.air).sub.=(ε).sup.1/2         (17)

where ε is the dielectric constant for air at microwave frequencies,which for dry air at STP, has the value ε_(STP) ⁻¹ =536.5×10⁻⁶. Hencethe frequency change from vacuum to air is of the order of 2.7×10⁻⁴.Since ε for dry air is accurately known at microwave frequencies as afunction of pressure and temperature, this shift can be corrected for toan accuracy of at least 1 part in 10⁶. The expression

    [(ε-1).sub.t,p /(ε-1).sub.20c, latm ]=(P/760)/[1+0.00341(t-20)]

can be used to correct for the pressure and temperature dependence of εto better than 0.1% accuracy. Since the perturbation in frequency isonly 2.7×10⁻⁴ initially, we can expect an overall accuracy in theresonant frequency determination of the order of 10⁻⁷ if the barometricpressure is monitored to better than 0.1% (or about 1 mm of mercury).

The water vapor (relative humidity) contribution to the dielectricconstant of air can be expressed as: ##EQU12## where T is thetemperature as measured by a precision temperature device in degreesKelvin and P is the partial pressure of water vapor in millibars. ForT=20° C. (293° K.), the saturation vapor pressure (100% relativehumidity) is 23 millibars. Hence, for this extreme case,

(√ε-1)_(water) vapor ×10⁻⁶ ≅100 which is approximately 1/3 as that fordry air. Again, this effect can be corrected to the 1st order bymeasurihng the relative humidity, and an accuracy of the order of 10⁻⁷can be achieved in determining the vacuum resonant frequency of thecavity.

Both the TE₁₁₁ and the TM₀₁₀ are not degenerate in frequency with anyother resonant TEM modes. Accidental degeneracy due to spuriousmode-crossing can be avoided by choosing the dimensions of the volumeproperly. The conditions for mode-crossing, between D/L>0 to D/L=3 are:

    D/L=0.45; D/L=1; and D/L=2.14

(at D/L=0.45, the TM₀₁₀ mode is degenerate with the TE₁₁₂ mode; atD/L=1, the TM₀₁₀ mode is degenerate with the TE₁₁₁ mode; at D/L=2.14,the TE₁₁₁ mode is degenerate with the TM₁₁₀ mode). Therefore, bychoosing D/L ratios other than those values, interactions with spuriousmodes are avoided and the resonant behavior of the cavity will bewell-defined and the formulas for calculating the resonant frequenciesfrom the dimensions of the chamber 28 are rigorously valid.

As an illustrative example, suppost we choose to work in the region of1<D/L<2.14 and require that the net traverse of the piston 14 displace avolume equal to 8 cu. ft. (2.2652×10⁵ cc). Then the followingconfiguration can be used:

D=104.88 cm

L₁ =52.44 cm=final piston position Y

L₂ =78.66 cm=initial piston position X.

Hence, the net displaced volume is, ##EQU13## Also, as can be seen, theD/L ratio varies from 1.33 for the initial position to 2 for the finalposition, which are well within the desirable operating range. For thiscase then:

f₁ =resonant frequency of TM₀₁₀ mode=219.0 Mc/s

f₂ (i)=initial value of TE₁₁₁ mode=253.9 Mc/s (D/L=1.33)

f₂ (f)=final value of TE₁₁₁ mode=331.5 Mc/s (D/L=2)

Similarly, for the case of 2 cubic feet total volume, the frequenciesare:

    f.sub.1 =347.6 Mc/s

    f.sub.2 (i)=403.0 Mc/s

    f.sub.2 (f)=526.2 Mc/s

The dependence of frequency for an incremental change in L can beexpressed as: ##EQU14## which for D/L=1.33 gives,

    (Δf/f)=1.1(ΔL/L)                               (20)

and for D/L=2 gives,

    (Δf/f)=1.5(ΔL/L).

As can be seen, the uncertainty in measuring L is nearly equal to thatfor the frequency measurement. Consequently, very high precision can beobtained for determining the volume displaced in this dimensionconfiguration.

It is also informative to estimate the quality factor Q of the resonantmodes, since the precision in measuring the resonant frequencies willdepend, to a great extent, on the sharpness of the resonances. For theTM₀₁₀ mode: ##EQU15## Where δ is the skin depth given by δ=[(λρ)/120π²μ]^(1/2), ρ is the resistivity of the wall material of the chamber 28, λis the wavelength, and μ is the permeability of the wall material.

If the chamber 28 is made of copper, ρ=1.7×10⁻⁶, μ=1 and δ=4.43×10⁻⁴ cmat 219 Mc/s. Therefore

    Q=6.8×10.sup.4 for D/L=1.33 and

    Q=5.9×10.sup.4 for D/L=2.

Depending in the coupling coefficient, the width of the resonance curveat the half power points varies between (2f_(o) /Q) and (f_(o) /Q) wheref_(o) is the resonant frequency. Consequently, the width of theresonance curve for the values of Q computed are:

at f_(o) =219 Mc/S: 3.2≦Δf≦6.4 kc/s for Q=6.8×10⁴

and

3.7≦Δf≦7.4 kc/s for Q=5.9×10⁴

Since f_(o) can be usually determined to an accuracy of 10⁻² of f orbetter, we can expect an accuracy of the order of 10⁻⁷ in determiningf_(o). This in turn implies accuracy of this order in the measurement ofthe diameter D of the chamber 28.

Similarly, for the TE₁₁₁ mode: ##EQU16## which gives, Q=7.5×10⁻⁴ at253.9 Mc/s and

Q=5.5×10⁻⁴ at 331.5 Mc/s.

As before, the widths of the resonance curves are,

3.4≦f≦6.8 kc/s at 253.9 Mc/s and

6.0≦f≦12.0 kc/s at 331.5 Mc/s.

Again adapting the criteria that f_(o) can be determined accurate to10⁻² of Δf, then for the worst case of (12.0 kc/s) Δf_(o) /f_(o)≈4×10⁻⁷. From the expression previously derived for D/L-2, ##EQU17##Therefore, (ΔL/L) can be determined to (4×10⁻⁷)/1.5≅2.7×10⁻⁷.

It is also possible to calculate the perturbation on the resonantfrequency of a cavity mode due to the presence of a gas-inlet and outletopening 62 on one head 60 of the cylinder 12. From the AdiabaticInvariance theorem and a knowledge of the field configuration inside thecavity, the frequency pulling caused by the hole can be estimated in astraightforward manner. If the hole dimension is well below the cut-offwavelength (which will be rigorously true for the case underconsideration), then the frequency pulling will be proportional to theratio of the cube of the hole diameter to the volume of the chamber 28.

Illustratively, the expression for the change in the resonant frequencyof the TM₀₁₀ mode caused by the opening 62 located at the center of theplate 60 is given by,

    (Δf/f.sub.o)=(d.sup.3)/8D.sup.2 L(X.sub.01)J.sub.1.sup.2 (X.sub.01) (21)

where d is the diameter of the hole J₁ (X₀₁) is the value of the Besselfunction J₁ at X₀₁, and Δf is the frequency shift.

Upon numerical evaluation using D=104.88 cm, L-52.44 cm, X₀₁ =2.40483and J₁ ² (X₀₁)=0.2695, then

    (Δf/f.sub.o)=3.35×10.sup.-7 d.sup.3

As can be seen, for d of the order of 2 cm or less, the frequency shiftis only of the order of 2×10⁻⁶. Consequently, the shift is very smalland with an appropriate initial calibration procedure, such as coveringthe opening 62 with a matching metallic plug, this effect can bevirtually eliminated as a systematic error in the precision of themethod.

Coupling of the microwave energy to the chamber 28 for the two modesTM₀₁₀ and TE₁₁₁ can best be accomplished by placing a coaxial feed lineterminated in the antenna 70 at a position approximately 1/2 way outfrom the center of the end plate 60 of the cylinder 12 with the looporiented along a radius. The magnetic field at this location is about90% of the maximum field intensity inside the cavity for both modes.Consequently, both modes are energized to the same degree of couplingwith high efficiency. In addition, by placing the coupling on the head60, the coupling will not be affected by the movement of thedisplacement piston 14.

In the following, a description will be given of a second preferredmethod of measuring a displacement volume within the chamber 28 andusing this accurately determined volume to calibrate the train of pulsesas provided by the optical, linear encoder 26. In a similar manner tothat described above, the piston 14 is moved from a first position asindicated in FIG. 10 by the designation L₁, to a second positionindicated by the designation L₂ having moved through a displacement ofΔL. The cylinder 12 is inherently rigid whereby the calibration process,as will be described, may be only carried out occasionally to insurethat no long term systematic changes, such as dimensional deformation ofthe cylinder 12, misalignment and malfunction of the optical linearencoder 26, or distortion of the piston 14 has occurred. In order tomaximize the absolute measurement accuracy of the microwave volumecalibration, it is necessary that the mechanical configuration of thecylinder 12 be as close as possible to that of a perfect, totallyenclosed right circular cylinder and thereby eliminate or reduce allpossible sources of systematic perturbations which could potentiallyaffect the microwave measurements.

Referring now to FIG. 12A, certain mechanical modifications are made.First, the physical gap that exists between the piston 14 and the wallsof the chamber 28 must be effectively blocked to prevent the escape ofmicrowave energy through that gap. As explained in the above-identifiedapplication, filed concurrently herewith and entitled "Piston Seal",because of the nature of the seal between the piston 14 and the wall ofthe chamber 28, the gap is considerable. A cover 11 is made of asuitable metallic material, such as stainless steel, and further, has aseries of springlike fingers 15, as shown in detail in FIG. 12B,disposed between the piston 14 and the inner periphery of the chamber28, which, when the cover 11 is in place over the piston 14, projectinto the gap between the piston 14 and the wall of the chamber 28, thefingers being in close contact with the piston 14 and the wall. Thefingers 15 act as a short circuit reflecting the electromagnetic fieldthat would otherwise be directed through the noted gap. In anillustrative embodiment, the springlike fingers 15 are made of aberyllium copper. Further, the pressure and temperature sensors 51, 57,48, and 68 are removed and are replaced by appropriate blank metallicplugs, configured to provide a substantially flush surface with theinside walls of the chamber 28. Further, the fluid inlet opening 62 inthe head 60 is covered by a metallic plate to provide a substantiallyflush surface across the the top of the head 60. In addition, the insideperipheral walls of the chamber 28 are cleaned with a suitable solventto remove any residual traces of the oil as may have seeped from thepiston seal. Noting that the required calibration is determined by adisplacement volume ΔV and not by the absolute volume of the chamber 28,the above-described mechanical modifications do not affect the accuracyof the calibration process. Once the measurements, as will be described,are made for the modified chamber 28, the same set of measurements maybe carried out immediately afterwards with the chamber 28 restored toits normal operating configuration and a set of appropriate calibrationfactors can be generated to relate the two sets of measurements. Theresults of the second measurements can then be used as a data base fromwhich subsequent checks of the absolute calibration can be comparedwithout going through the full procedure of modification and reassemblyof the chamber 28.

Briefly, the volume measuring and calibration process includes the stepof moving the piston 14 to a first position indicated by the designationL₁ in FIG. 10, by manually rotating the rotary member 19 of theservomotor 20. At the first position, the antenna 70 is energized withelectromagnetic energy of a first mode TE₁₁₁ and a second mode TE₁₁₂,selected to minimize the above-discussed perturbations. The frequenciesf₁ and f₂ at which resonance is established for each mode is detected byobserving the counter 1108. Then, the piston 14 is moved through adistant ΔL to a second position as indicated by the designation L₂,whereat the antenna 70 is energized again with electromagnetic energy ofthe first and second modes and corresponding frequencies at whichresonance is established for each of the modes are noted. The output ofthe optical, linear encoder 26 is applied to a counter, which counts thelinear encoder pulses as the piston 14 is moved through the distance ΔL.The diameters D₁ and D₂ of the chamber 28 at each of the first andsecond positions corresponding to the designations L₁ and L₂ arecalculated. At this point, a calculation of the ΔL is made using thepreviously calculated values of D₁ and D₂. The calculated value of ΔL isdivided by the number of pulses derived from the linear encoder 26 ascounted during the movement of the piston 14 through the distance ΔL toprovide a length calibration factor using the measurements of D₁ and D₂.The volume ΔV corresponding to that volume as defined by planes passingthrough the points L₁ and L₂ and the inner periphery of the chamber 28is expressed by a mathematical expression in terms of the diameters D₁and D₂ and ΔL. If the output of the optical, linear encoder 26 is to becalibrated for a given volume, e.g., one cubic foot, that value isdisposed in this equation and it is solved for the calculated values D₁and D₂ to provide that value of ΔL corresponding to the movement of thepiston 14 to draw one cubic foot of fluid through the meter 38. Thecalculated value of ΔL is multiplied by the previously calculated lengthcalibration factor to provide that number of pulses that will be outputby the optical, linear encoder 26 as the piston 14 is moved a length ΔLto draw the one cubic foot into the chamber 28. As explained above, thecount as derived from the linear encoder 26 is used to calculate thecalibration factor as incorporated within the calculation carried out instep 1062, as shown in FIG. 9N. In particular, the calibration factor isthe reciprocal of the counts so derived for one cubic foot of fluiddrawn into the chamber 28 and provides a correction to the calculationof percent error in the reading of the meter based upon a precisemeasurement of the volume of the chamber 28, as explained above.

First, it is necessary to measure the frequencies at which the standingwave conditions are established at the positions L₁ and L₂. Thecalculation of diameters D₁ and D₂, as will be explained, requires avalue of the speed of light, which changes for varying ambientconditions of temperature, pressure, and relative humidity. Correctionsfor changes in the speed of light are expected to be small, and thecalculation of the speed of light is made typically once or twice duringthe course of a calibration process of the optical, linear encoder 26.

The speed of light in vacuum, Co, is 2.997925×10¹⁰ cm/sec. Thecorresponding value c for air is obtained by dividing Co by therefractive index of air at the wavelength of observation. For themicrowave region (f<30 GHz), the refractive index, n, is related to theatmospheric parameters by the equation: ##EQU18## where P is the totalpressures in millibars (1 bar=10⁶ dynes/cm² =0.986923 standardatmosphere -75.0062 cm Hg at 0° C.), T is the temperature in degreesKelvin, and e is the partial vapor pressure of water in millibars. Thespeed of light is then given by ##EQU19##

The temperature and barometric pressure can be directly obtained fromthe readings of a thermometer and a barometer placed near the meterprover 10. The partial vapor pressure of water can be deduced from therelative humidity data obtained with a sling psychrometer through theuse of the psychrometer formula, or more conveniently, via the use of astandard table such as the Smithsonian Physical Table #640.

In order to calculate a value of ΔL, there is needed to determine theaverage value of the diameter of the chamber 28 and more specifically,to determine the values of the diameters D₁ and D₂ at the locations L₁and L₂, respectively. The calculation D₁ and D₂ is carried out withgreat care since the resulting uncertainty in the volume isapproximately twice the uncertainty of this measurement. As explainedabove, the piston 14 is moved to the first position corresponding to thedesignation L₁ at which the frequencies f₁ and f₂ for which the resonantstanding wave condition is established for the two different modes. Thepreferred method is to measure simultaneously the resonant frequenciesf₁ and f₂ of two different modes of the same electrical characteristicsas a function of the piston position L and solve for the averagediameter D by using the appropriate theoretical expression.

In a preferred embodiment wherein the chamber 28 has the configurationof a right circular cylinder, the pair of modes preferred for thispurpose are the TE₁₁₁ and TE₁₁₂ modes. As will be discussed, it has beendemonstrated that the quality factor Q obtained by excitation in thesemodes is high thereby reducing the effects of perturbations upon themeasurements of resonant frequency. The average diameter of the cylinderat any fixed position of L is given by the expression: ##EQU20## wheref₂ is the resonant frequency of the TE₁₁₁ mode and f₁ is the resonantfrequency of the TE₁₁₂ mode, and c is the speed of light in air ascalculated by equation 23. By using two different modes ofelectromagnetic wave energy excitation, the various perturbations suchas skin-depth variation, reactive frequency pulling caused by theantenna 70, the degree of divergency of the inner periphery of thechamber 28 from being a perfect right circular cylinder are compensatedfor and the absolute value of D is obtained with great accuracy. Byexercising care in the taking of measurements of the frequencies uponthe counter 1108, as shown in FIG. 10, absolute accuracies of the valuesD as a function of L may be obtained in the order of one part in 10⁵ or0.1 mill out of a 12 inch diameter. This degree of accuracy is of thesame order of the changes in the volume of the chamber 28 due to thermalexpansion and contraction as disposed in a temperature stabilizedenvironment where the temperature is maintained within range of ±1° F.

In order to confirm these measurements as well as to provide aquantitative means for evaluation of the order of magnitude of theexpected perturbations in the system of measurement, the diameter may beindependently determined by measuring the resonant wave frequencies bygenerating electromagnetic waves of the TM₀₁₀ mode within the chamber28. With such a mode of excitation, the resonant frequency isindependent of the length L and therefore for a perfectly uniformcylinder, should not change as the position of piston 14 is varied.However, excitation in the TM₀₁₀ mode is subject to other variousperturbations which need be considered to achieve the same degree ofaccuracy as for the two modes discussed above. For the TM₀₁₀ mode, theaverage diameter is given by the expression:

    D(L)=0.7654799c/f                                          (25)

where f is a resonant frequency of the TM₀₁₀ mode.

Once the average diameter D of the chamber 28 as a function of L hasbeen determined to the desired degree of accuracy, the value of ΔL isobtained and related to the observed number of pulses from the optical,linear encoder 26 in order to obtain the length calibration factor interms of length per pulse interval or number of pulses per inch. Thepiston position is set at L₁, and the resonant frequencies at f₁ and f₂for the selected modes TE₁₁₁ and TE₁₁₂ are measured. The piston 14 isthen moved by cranking the rotary member 19 to a new position L₂ and theresonant frequencies of the same modes are remeasured, while countingthe number of optical encoder pulses during the movement of the piston14 from its first to its second position. The number of pulses isdivided by ΔL=L₁ -L₂ to provide the desired length calibration factor.The distance ΔL=(L₁ -L₂) should be large enough such that thecalibration accuracy is not limited by the accuracy in the pulse count(±1 in this case) and the calibration should be performed over a numberof ΔL intervals to insure that no non-linearity effects exist in thesemeasurements.

For the TE₁₁₁ mode, the change in distance ΔL is given by theexpression: ##EQU21## where f₂ and D(L₂) are the TE₁₁₁ mode resonantfrequency and the previously determined average diameter at pistonposition L₂, and f₁ and D(L₁) are the respective values at position L₁.

For the TE₁₁₂ mode, the change in distance ΔL is given by theexpression: ##EQU22## where the various quantities are defined in asimilar manner as above.

Similar expressions can be written for any mode of excitation, and morethan one mode can be used to check the internal consistency and absoluteaccuracy of these measurements.

The absolute calibration of the displacement volume ΔV between thepiston positions L₁ and L₂ is provided by the following expression:

    ΔV=V.sub.2 -V.sub.1 (π/4)[D.sub.2.sup.2 (ΔL)+(D.sub.2.sup.2 -D.sub.1.sup.2)L.sub.1 ]                                  (28)

where D₂ and D₁ are the averaged diameters of the cylindricalcross-sections as taken at piston positions L₁ and L₂ and DL=(L₁ -L₂).It is evident from an observation of the equation 28 that knowing valuesof D₂ and D₁, if we assume for calibration purposes a given value of theabsolute displacement volume ΔV, e.g., one cubic foot, that thecorresponding value of ΔL, i.e., that distance through which the piston14 must be moved in order to draw one cubic foot of fluid into thechamber 28 of the meter prover 12, may be calculated. The object of thecalibration is to obtain the number of pulses as derived from theoptical linear encoder 26 that are output for any desired displacementvolume ΔV and is obtained by multiplying the obtained value of ΔL for agiven volume by the length calibration factor to provide the equivalentnumber of pulses that are output by the optical linear encoder 26.

The selection of the TE₁₁₁ and TE₁₁₂ modes to excite the cavity 28 wasbased upon repeated determinations using a number of normal moderesonances to determine the quality factor Q for each of the modes.These determinations of the Q of a normal mode require the measurementsof the ratio of the reflected power (Pr) to the incident (Po) at theresonant frequency, and the frequency width of the response curvecorresponding to the half-power level defined by P_(1/2) =(Po+Pr)/2. Itis desired that the d.c. voltage response of the crystal detector 1110be linear with input microwave power. This condition can be satisfied byoperating the crystal detector 1110 in the so-called "square lawdetection" region corresponding to a d.c. level typically less than 20millivolt. If necessary, the linearity of the response can be verifiedby the use of the step attenuator located on the sweep generator 1100.Once established, the coupling coefficient (Pr/Po) can be measureddirectly on the screen of the oscilloscope 1112 in terms of thecorresponding voltage ratio. The half-power level then can be calculatedas an equivalent voltage. The half width of the response curve, as shownin FIG. 14, is just the difference between the two frequency settings asset on the sweep generator 1100 corresponding to the half-power levelson either side of the resonant frequency as observed on the oscilloscope1112. The Q of the resonance is calculated by using the expression givenby equation 10. From these determinations of Q, it was demonstrated thatTE₁₁₁ mode has a quality factor Q of approximatey 6,000 to 7,000 overthe running range of the piston 14, while the TE₁₁₂ mode has a qualityfactor Q of 8,000 to 10,000. As indicated above, the quality factor is ameasure of the order of magnitude of the expected deviation of theresonant frequency from the idealized results as provided by equation 1.Thus by using these modes, the resonant frequency may be measured with agreater accuracy and those perturbations as would arise due to insurface imperfections as well as for the effects of skin depth andfrequency pulling may be minimized. Thus, the use of the modes TE₁₁₁ andTE₁₁₂ are believed to provide determinations of greater accuracy of theresonant frequency, and thus of the average diameter D and of the volumedisplacement between the two piston positions.

Thus, there has been described a meter prover that is capable ofmeasuring fluid and in particular, gas flow through a meter with a highdegree of precision. In one aspect of this invention, the volume of thecylinder into which the fluid is drawn is measured with extreme accuracyand is compared to the output of the encoder which detects movement ofthe cylinder's piston, whereby indication of the volume drawn into thecylinder is provided with corresponding high degree of accuracy. Thisstandard or calibrated volume is compared with the output of the meterunder test to provide an indication of meter registration, as well asthe percentage of error of the meter fluid reading from the actual orcalibrated volume indicated by the optical encoder of the meter proversystem. Further, the meter prover system is controlled by a computersystem whereby a number of tests are made in which parameters of meterand prover temperature and pressure are taken into consideration toadjust the indication of the measured volume of fluid flow, as well asto take repeated tests under varying conditions. In particular, varyingvolumes of fluid may be drawn by the meter prover through the meter byentering corresponding count factors into a counter of the computer andcounting the selected count to zero, to terminate the meter test. In afurther aspect of this invention, a new and novel method is employed fordetermining with high precision the volume of the cylinder into whichthe fluid is drawn for a given displacement of the piston. This accuratemeasurement is determined by the frequencies at which standing waves areestablished for first and second piston positions to provide a preciseindication of the fluid volume and the output of the optical encodercoupled to detect the movement of the piston.

Numerous changes may be made in the above-described apparatus andmethod, and different embodiments of the invention may be made withoutdeparting from the spirit thereof; therefore, it is intended that allmatter contained in the foregoing description and the accompanyingdrawings shall be interpreted as illustrative and not in a limitingsense.

We claim:
 1. Apparatus for measuring with a high degree of accuracy thevolume of a chamber of a meter prover, said chamber having the regulargeometry of a right circular cylinder, the volume of said right circularcylinder being defined its diameter and length, said measuring apparatuscomprising;(a) antenna means disposed for generating electromagneticenergy into and for receiving electromagnetic energy reflected from saidchamber; (b) generating means coupled to said antenna means forgenerating first and second resonant modes of selected electromagneticenergy fields, each of said first and second modes having anelectromagnetic energy field whose electric and magnetic componentfields are uniquely related to said diameter and said length of saidright circular cylinder; (c) means coupled to said antenna means fordetecting the electromagnetic energy reflected from said right circularcylinder; (d) resonant condition detecting means coupled to said energydetecting means for providing first and second indications of theoccurrences of the minimum levels of the reflected electromagneticenergy corresponding to the establishment of a standing wave resonantcondition within said right circular cylinder for each of said first andsecond resonant modes; and (e) means coupled to said generating meansfor detecting first and second frequencies at which said standing waveresonant conditions are established within said right circular cylinder,said first and second frequencies being a function of the volume of saidright circular cylinder whereby said volume is defined with the highdegree of accuracy.
 2. Volume measuring apparatus as claimed in claim 1,wherein said generating means comprises means for varying the frequencyof the microwave electromagnetic energy until a standing wave conditionis established within the chamber.
 3. Volume measuring apparatus asclaimed in claim 2, wherein said generating means automatically variesthe frequency of the output microwave electromagnetic energy.
 4. Volumemeasuring apparatus as claimed in claim 2, wherein said generating meanscomprises operator manipulable means for varying the frequency of theoutputted electromagnetic wave energy.
 5. Volume measuring apparatus asclaimed in claim 1, wherein said energy detecting means and saidgenerating means are each coupled to said antenna means and to saidresonant condition detecting means, whereby a manifestation of the levelof energy leaving said chamber is provided as a function of thefrequency of the electromagnetic energy generated by saidelectromagnetic generating means.
 6. Volume measuring apparatus asclaimed in claim 1, wherein said detecting means comprises a counter. 7.Volume measuring apparatus as claimed in claim 1, wherein there isincluded means coupled to the output of said electromagnetic energygenerating means for detecting the level of energy and for providing afeedback signal indicative of the level of energy to saidelectromagnetic energy generating means, whereby the level of powerrequired by said electromagnetic energy generating means is stabilized.8. A method of measuring accurately the volume of a meter prover, themeter prover including a chamber having the geometry of a right circularcylinder and dimensions including its diameter and axial length to bemeasured, said method comprising the steps of:(a) selecting at least oneresonant mode of an electromagnetic field having electric and magneticcomponent fields that are uniquely related to the diameter and axiallength of said chamber, (b) generating first and second distinct normalmodes of electromagnetic energy field within said chamber of saidselected resonant mode; (c) extracting reflected energy from saidregular geometry chamber; (d) sensing first and second frequencies ofthe electromagnetic energy that establish resonant conditions for thefirst and second modes within said chamber; and (e) determining, basedupon the numerical values of the sensed first and second frequencies,the length and diameter of and thus the volume of the right circularcylinder chamber.
 9. The method of measuring volume as claimed in claim8, wherein the normal modes for generating electromagnetic energy areselected to minimize the perturbations due to the character,configuration, and surface of the chamber.
 10. The method of measuringvolume as claimed in claim 9, wherein the modes selected are the TE₁₁₁mode and the TE₁₁₂ mode.
 11. The method of measuring volume as claimedin claim 9, wherein the modes selected are the TE₁₁₂ mode and the TM₀₁₀mode.
 12. The method of measuring volume as claimed in claim 9 whereinthe modes selected are the TM₀₁₀ mode and the TE₁₁₁ mode.
 13. A methodof measuring accurately the volume of a chamber having the geometry of aright circular cylinder, the volume of said right circular cylinderbeing defined by its diameter and length, said method comprising thesteps of:(a) selecting two resonant modes of electromagnetic energyfields, each of said modes having an electromagnetic energy field whoseelectric and magnetic component fields are uniquely related to saiddiameter and said length of said right circular cylinder; (b) generatingsaid two electromagnetic energy fields of said two selected resonantmodes, respectively; (d) extracting reflected energy from said rightcircular cylinder for each of said two electromagnetic energy fields;(d) sensing two frequencies of the electromagnetic energy fields thatestablish resonant conditions for said two normal modes respectivelywithin said right circular cylinder; and (e) determining, based uponsaid two sensed resonant frequencies, said length and said diameter ofand thus the volume of said right circular cylinder.